Package list python-pyqrcode / debian/1.2.1-2 pyqrcode / builder.py
debian/1.2.1-2

Tree @debian/1.2.1-2 (Download .tar.gz)

builder.py @debian/1.2.1-2raw · history · blame

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
# -*- coding: utf-8 -*-
# Copyright (c) 2013, Michael Nooner
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above copyright
#       notice, this list of conditions and the following disclaimer in the
#       documentation and/or other materials provided with the distribution.
#     * Neither the name of the copyright holder nor the names of its 
#       contributors may be used to endorse or promote products derived from
#       this software without specific prior written permission
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
# DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""This module does the actual generation of the QR codes. The QRCodeBuilder
builds the code. While the various output methods draw the code into a file.
"""

#Imports required for 2.x support
from __future__ import absolute_import, division, print_function, with_statement, unicode_literals

import pyqrcode.tables as tables
import io
import itertools
import math

class QRCodeBuilder:
    """This class generates a QR code based on the standard. It is meant to
    be used internally, not by users!!!

    This class implements the tutorials found at:

    * http://www.thonky.com/qr-code-tutorial/

    * http://www.matchadesign.com/blog/qr-code-demystified-part-6/

    This class also uses the standard, which can be read online at:
        http://raidenii.net/files/datasheets/misc/qr_code.pdf

    Test codes were tested against:
        http://zxing.org/w/decode.jspx

    Also, reference codes were generat/ed at:
        http://www.morovia.com/free-online-barcode-generator/qrcode-maker.php
        http://demos.telerik.com/aspnet-ajax/barcode/examples/qrcode/defaultcs.aspx

    QR code Debugger:
        http://qrlogo.kaarposoft.dk/qrdecode.html
    """
    def __init__(self, data, version, mode, error):
        """See :py:class:`pyqrcode.QRCode` for information on the parameters."""
        #Set what data we are going to use to generate
        #the QR code
        self.data = data

        #Check that the user passed in a valid mode
        if mode in tables.modes:
            self.mode = tables.modes[mode]
        else:
            raise ValueError('{0} is not a valid mode.'.format(mode))

        #Check that the user passed in a valid error level
        if error in tables.error_level:
            self.error = tables.error_level[error]
        else:
            raise ValueError('{0} is not a valid error '
                             'level.'.format(error))

        if 1 <= version <= 40:
            self.version = version
        else:
            raise ValueError("Illegal version {0}, version must be between "
                             "1 and 40.".format(version))

        #Look up the proper row for error correction code words
        self.error_code_words = tables.eccwbi[version][self.error]

        #This property will hold the binary string as it is built
        self.buffer = io.StringIO()

        #Create the binary data block
        self.add_data()

        #Create the actual QR code
        self.make_code()

    def grouper(self, n, iterable, fillvalue=None):
        """This generator yields a set of tuples, where the
        iterable is broken into n sized chunks. If the
        iterable is not evenly sized then fillvalue will
        be appended to the last tuple to make up the difference.

        This function is copied from the standard docs on
        itertools.
        """
        args = [iter(iterable)] * n
        if hasattr(itertools, 'zip_longest'):
            return itertools.zip_longest(*args, fillvalue=fillvalue)
        return itertools.izip_longest(*args, fillvalue=fillvalue)

    def binary_string(self, data, length):
        """This method returns a string of length n that is the binary
        representation of the given data. This function is used to
        basically create bit fields of a given size.
        """
        return '{{0:0{0}b}}'.format(length).format(int(data))

    def get_data_length(self):
        """QR codes contain a "data length" field. This method creates this
        field. A binary string representing the appropriate length is
        returned.
        """

        #The "data length" field varies by the type of code and its mode.
        #discover how long the "data length" field should be.
        if 1 <= self.version <= 9:
            max_version = 9
        elif 10 <= self.version <= 26:
            max_version = 26
        elif 27 <= self.version <= 40:
            max_version = 40

        data_length = tables.data_length_field[max_version][self.mode]

        if self.mode != tables.modes['kanji']:
            length_string = self.binary_string(len(self.data), data_length)
        else:
            length_string = self.binary_string(len(self.data) / 2, data_length)

        if len(length_string) > data_length:
            raise ValueError('The supplied data will not fit '
                               'within this version of a QRCode.')
        return length_string

    def encode(self):
        """This method encodes the data into a binary string using
        the appropriate algorithm specified by the mode.
        """
        if self.mode == tables.modes['alphanumeric']:
            encoded = self.encode_alphanumeric()
        elif self.mode == tables.modes['numeric']:
            encoded = self.encode_numeric()
        elif self.mode == tables.modes['binary']:
            encoded = self.encode_bytes()
        elif self.mode == tables.modes['kanji']:
            encoded = self.encode_kanji()
        return encoded

    def encode_alphanumeric(self):
        """This method encodes the QR code's data if its mode is
        alphanumeric. It returns the data encoded as a binary string.
        """
        #Convert the string to upper case
        self.data = self.data.upper()

        #Change the data such that it uses a QR code ascii table
        ascii = []
        for char in self.data:
            if isinstance(char, int):
                ascii.append(tables.ascii_codes[chr(char)])
            else:
                ascii.append(tables.ascii_codes[char])
        
        #Now perform the algorithm that will make the ascii into bit fields
        with io.StringIO() as buf:
            for (a,b) in self.grouper(2, ascii):
                if b is not None:
                    buf.write(self.binary_string((45*a)+b, 11))
                else:
                    #This occurs when there is an odd number
                    #of characters in the data
                    buf.write(self.binary_string(a, 6))

            #Return the binary string
            return buf.getvalue()

    def encode_numeric(self):
        """This method encodes the QR code's data if its mode is
        numeric. It returns the data encoded as a binary string.
        """
        with io.StringIO() as buf:
            #Break the number into groups of three digits
            for triplet in self.grouper(3, self.data):
                number = ''
                for digit in triplet:
                    if isinstance(digit, int):
                        digit = chr(digit)

                    #Only build the string if digit is not None
                    if digit:
                        number = ''.join([number, digit])
                    else:
                        break

                #If the number is one digits, make a 4 bit field
                if len(number) == 1:
                    bin = self.binary_string(number, 4)

                #If the number is two digits, make a 7 bit field
                elif len(number) == 2:
                    bin = self.binary_string(number, 7)

                #Three digit numbers use a 10 bit field
                else:
                    bin = self.binary_string(number, 10)

                buf.write(bin)
            return buf.getvalue()

    def encode_bytes(self):
        """This method encodes the QR code's data if its mode is
        8 bit mode. It returns the data encoded as a binary string.
        """
        with io.StringIO() as buf:
            for char in self.data:
                if not isinstance(char, int):
                    buf.write('{{0:0{0}b}}'.format(8).format(ord(char)))
                else:
                    buf.write('{{0:0{0}b}}'.format(8).format(char))
            return buf.getvalue()

    def encode_kanji(self):
        """This method encodes the QR code's data if its mode is
        kanji. It returns the data encoded as a binary string.
        """
        def two_bytes(data):
            """Output two byte character code as a single integer."""
            def next_byte(b):
                """Make sure that character code is an int. Python 2 and
                3 compatibility.
                """
                if not isinstance(b, int):
                    return ord(b)
                else:
                    return b

            #Go through the data by looping to every other character
            for i in range(0, len(data), 2):
                yield (next_byte(data[i]) << 8) | next_byte(data[i+1])

        #Force the data into Kanji encoded bytes
        if isinstance(self.data, bytes):
            data = self.data.decode('shiftjis').encode('shiftjis')
        else:
            data = self.data.encode('shiftjis')
        
        #Now perform the algorithm that will make the kanji into 13 bit fields
        with io.StringIO() as buf:
            for asint in two_bytes(data):
                #Shift the two byte value as indicated by the standard
                if 0x8140 <= asint <= 0x9FFC:
                    difference = asint - 0x8140
                elif 0xE040 <= asint <= 0xEBBF:
                    difference = asint - 0xC140

                #Split the new value into most and least significant bytes
                msb = (difference >> 8)
                lsb = (difference & 0x00FF)

                #Calculate the actual 13 bit binary value
                buf.write('{0:013b}'.format((msb * 0xC0) + lsb))
            #Return the binary string
            return buf.getvalue()


    def add_data(self):
        """This function properly constructs a QR code's data string. It takes
        into account the interleaving pattern required by the standard.
        """
        #Encode the data into a QR code
        self.buffer.write(self.binary_string(self.mode, 4))
        self.buffer.write(self.get_data_length())
        self.buffer.write(self.encode())

        #Converts the buffer into "code word" integers.
        #The online debugger outputs them this way, makes
        #for easier comparisons.
        #s = self.buffer.getvalue()
        #for i in range(0, len(s), 8):
        #    print(int(s[i:i+8], 2), end=',')
        #print()
        
        #Fix for issue #3: https://github.com/mnooner256/pyqrcode/issues/3#
        #I was performing the terminate_bits() part in the encoding.
        #As per the standard, terminating bits are only supposed to
        #be added after the bit stream is complete. I took that to
        #mean after the encoding, but actually it is after the entire
        #bit stream has been constructed.
        bits = self.terminate_bits(self.buffer.getvalue())
        if bits is not None:
            self.buffer.write(bits)

        #delimit_words and add_words can return None
        add_bits = self.delimit_words()
        if add_bits:
            self.buffer.write(add_bits)
        
        fill_bytes = self.add_words()
        if fill_bytes:
            self.buffer.write(fill_bytes)
        
        #Get a numeric representation of the data
        data = [int(''.join(x),2)
                    for x in self.grouper(8, self.buffer.getvalue())]

        #This is the error information for the code
        error_info = tables.eccwbi[self.version][self.error]

        #This will hold our data blocks
        data_blocks = []

        #This will hold our error blocks
        error_blocks = []

        #Some codes have the data sliced into two different sized blocks
        #for example, first two 14 word sized blocks, then four 15 word
        #sized blocks. This means that slicing size can change over time.
        data_block_sizes = [error_info[2]] * error_info[1]
        if error_info[3] != 0:
            data_block_sizes.extend([error_info[4]] * error_info[3])

        #For every block of data, slice the data into the appropriate
        #sized block
        current_byte = 0
        for n_data_blocks in data_block_sizes:
            data_blocks.append(data[current_byte:current_byte+n_data_blocks])
            current_byte += n_data_blocks
        
        #I am not sure about the test after the "and". This was added to
        #fix a bug where after delimit_words padded the bit stream, a zero
        #byte ends up being added. After checking around, it seems this extra
        #byte is supposed to be chopped off, but I cannot find that in the
        #standard! I am adding it to solve the bug, I believe it is correct.
        if current_byte < len(data):
            raise ValueError('Too much data for this code version.')

        #DEBUG CODE!!!!
        #Print out the data blocks
        #print('Data Blocks:\n{0}'.format(data_blocks))

        #Calculate the error blocks
        for n, block in enumerate(data_blocks):
            error_blocks.append(self.make_error_block(block, n))

        #DEBUG CODE!!!!
        #Print out the error blocks
        #print('Error Blocks:\n{0}'.format(error_blocks))

        #Buffer we will write our data blocks into
        data_buffer = io.StringIO()

        #Add the data blocks
        #Write the buffer such that: block 1 byte 1, block 2 byte 1, etc.
        largest_block = max(error_info[2], error_info[4])+error_info[0]
        for i in range(largest_block):
            for block in data_blocks:
                if i < len(block):
                    data_buffer.write(self.binary_string(block[i], 8))

        #Add the error code blocks.
        #Write the buffer such that: block 1 byte 1, block 2 byte 2, etc.
        for i in range(error_info[0]):
            for block in error_blocks:
                data_buffer.write(self.binary_string(block[i], 8))

        self.buffer = data_buffer

    def terminate_bits(self, payload):
        """This method adds zeros to the end of the encoded data so that the
        encoded data is of the correct length. It returns a binary string
        containing the bits to be added.
        """
        data_capacity = tables.data_capacity[self.version][self.error][0]

        if len(payload) > data_capacity:
            raise ValueError('The supplied data will not fit '
                             'within this version of a QR code.')

        #We must add up to 4 zeros to make up for any shortfall in the
        #length of the data field.
        if len(payload) == data_capacity:
            return None
        elif len(payload) <= data_capacity-4:
            bits = self.binary_string(0,4)
        else:
            #Make up any shortfall need with less than 4 zeros
            bits = self.binary_string(0, data_capacity - len(payload))

        return bits

    def delimit_words(self):
        """This method takes the existing encoded binary string
        and returns a binary string that will pad it such that
        the encoded string contains only full bytes.
        """
        bits_short = 8 - (len(self.buffer.getvalue()) % 8)
        
        #The string already falls on an byte boundary do nothing
        if bits_short == 0 or bits_short == 8:
            return None
        else:
            return self.binary_string(0, bits_short)

    def add_words(self):
        """The data block must fill the entire data capacity of the QR code.
        If we fall short, then we must add bytes to the end of the encoded
        data field. The value of these bytes are specified in the standard.
        """

        data_blocks = len(self.buffer.getvalue()) // 8
        total_blocks = tables.data_capacity[self.version][self.error][0] // 8
        needed_blocks = total_blocks - data_blocks

        if needed_blocks == 0:
            return None

        #This will return item1, item2, item1, item2, etc.
        block = itertools.cycle(['11101100', '00010001'])

        #Create a string of the needed blocks
        return ''.join([next(block) for x in range(needed_blocks)])

    def make_error_block(self, block, block_number):
        """This function constructs the error correction block of the
        given data block. This is *very complicated* process. To
        understand the code you need to read:

        * http://www.thonky.com/qr-code-tutorial/part-2-error-correction/
        * http://www.matchadesign.com/blog/qr-code-demystified-part-4/
        """
        #Get the error information from the standards table
        error_info = tables.eccwbi[self.version][self.error]

        #This is the number of 8-bit words per block
        if block_number < error_info[1]:
            code_words_per_block = error_info[2]
        else:
            code_words_per_block = error_info[4]

        #This is the size of the error block
        error_block_size = error_info[0]

        #Copy the block as the message polynomial coefficients
        mp_co = block[:]

        #Add the error blocks to the message polynomial
        mp_co.extend([0] * (error_block_size))

        #Get the generator polynomial
        generator = tables.generator_polynomials[error_block_size]

        #This will hold the temporary sum of the message coefficient and the
        #generator polynomial
        gen_result = [0] * len(generator)

        #Go through every code word in the block
        for i in range(code_words_per_block):
            #Get the first coefficient from the message polynomial
            coefficient = mp_co.pop(0)

            #Skip coefficients that are zero
            if coefficient == 0:
                continue
            else:
                #Turn the coefficient into an alpha exponent
                alpha_exp = tables.galois_antilog[coefficient]

            #Add the alpha to the generator polynomial
            for n in range(len(generator)):
                gen_result[n] = alpha_exp + generator[n]
                if gen_result[n] > 255:
                    gen_result[n] = gen_result[n] % 255

                #Convert the alpha notation back into coefficients
                gen_result[n] = tables.galois_log[gen_result[n]]

                #XOR the sum with the message coefficients
                mp_co[n] = gen_result[n] ^ mp_co[n]

        #Pad the end of the error blocks with zeros if needed
        if len(mp_co) < code_words_per_block:
            mp_co.extend([0] * (code_words_per_block - len(mp_co)))

        return mp_co

    def make_code(self):
        """This method returns the best possible QR code."""
        from copy import deepcopy

        #Get the size of the underlying matrix
        matrix_size = tables.version_size[self.version]

        #Create a template matrix we will build the codes with
        row = [' ' for x in range(matrix_size)]
        template = [deepcopy(row) for x in range(matrix_size)]

        #Add mandatory information to the template
        self.add_detection_pattern(template)
        self.add_position_pattern(template)
        self.add_version_pattern(template)

        #Create the various types of masks of the template
        self.masks = self.make_masks(template)

        self.best_mask = self.choose_best_mask()
        self.code = self.masks[self.best_mask]

    def add_detection_pattern(self, m):
        """This method add the detection patterns to the QR code. This lets
        the scanner orient the pattern. It is required for all QR codes.
        The detection pattern consists of three boxes located at the upper
        left, upper right, and lower left corners of the matrix. Also, two
        special lines called the timing pattern is also necessary. Finally,
        a single black pixel is added just above the lower left black box.
        """

        #Draw outer black box
        for i in range(7):
            inv = -(i+1)
            for j in [0,6,-1,-7]:
                m[j][i] = 1
                m[i][j] = 1
                m[inv][j] = 1
                m[j][inv] = 1

        #Draw inner white box
        for i in range(1, 6):
            inv = -(i+1)
            for j in [1, 5, -2, -6]:
                m[j][i] = 0
                m[i][j] = 0
                m[inv][j] = 0
                m[j][inv] = 0

        #Draw inner black box
        for i in range(2, 5):
            for j in range(2, 5):
                inv = -(i+1)
                m[i][j] = 1
                m[inv][j] = 1
                m[j][inv] = 1

        #Draw white border
        for i in range(8):
            inv = -(i+1)
            for j in [7, -8]:
                m[i][j] = 0
                m[j][i] = 0
                m[inv][j] = 0
                m[j][inv] = 0

        #To keep the code short, it draws an extra box
        #in the lower right corner, this removes it.
        for i in range(-8, 0):
            for j in range(-8, 0):
                m[i][j] = ' '

        #Add the timing pattern
        bit = itertools.cycle([1,0])
        for i in range(8, (len(m)-8)):
            b = next(bit)
            m[i][6] = b
            m[6][i] = b

        #Add the extra black pixel
        m[-8][8] = 1

    def add_position_pattern(self, m):
        """This method draws the position adjustment patterns onto the QR
        Code. All QR code versions larger than one require these special boxes
        called position adjustment patterns.
        """
        #Version 1 does not have a position adjustment pattern
        if self.version == 1:
            return

        #Get the coordinates for where to place the boxes
        coordinates = tables.position_adjustment[self.version]

        #Get the max and min coordinates to handle special cases
        min_coord = coordinates[0]
        max_coord = coordinates[-1]

        #Draw a box at each intersection of the coordinates
        for i in coordinates:
            for j in coordinates:
                #Do not draw these boxes because they would
                #interfere with the detection pattern
                if (i == min_coord and j == min_coord) or \
                   (i == min_coord and j == max_coord) or \
                   (i == max_coord and j == min_coord):
                    continue

                #Center black pixel
                m[i][j] = 1

                #Surround the pixel with a white box
                for x in [-1,1]:
                    m[i+x][j+x] = 0
                    m[i+x][j] = 0
                    m[i][j+x] = 0
                    m[i-x][j+x] = 0
                    m[i+x][j-x] = 0

                #Surround the white box with a black box
                for x in [-2,2]:
                    for y in [0,-1,1]:
                        m[i+x][j+x] = 1
                        m[i+x][j+y] = 1
                        m[i+y][j+x] = 1
                        m[i-x][j+x] = 1
                        m[i+x][j-x] = 1

    def add_version_pattern(self, m):
        """For QR codes with a version 7 or higher, a special pattern
        specifying the code's version is required.

        For further information see:
        http://www.thonky.com/qr-code-tutorial/format-version-information/#example-of-version-7-information-string
        """
        if self.version < 7:
            return

        #Get the bit fields for this code's version
        #We will iterate across the string, the bit string
        #needs the least significant digit in the zero-th position
        field = iter(tables.version_pattern[self.version][::-1])

        #Where to start placing the pattern
        start = len(m)-11

        #The version pattern is pretty odd looking
        for i in range(6):
            #The pattern is three modules wide
            for j in range(start, start+3):
                bit = int(next(field))

                #Bottom Left
                m[i][j] = bit

                #Upper right
                m[j][i] = bit

    def make_masks(self, template):
        """This method generates all seven masks so that the best mask can
        be determined. The template parameter is a code matrix that will
        server as the base for all the generated masks.
        """
        from copy import deepcopy

        nmasks = len(tables.mask_patterns)
        masks = [''] * nmasks
        count = 0

        for n in range(nmasks):
            cur_mask = deepcopy(template)
            masks[n] = cur_mask

            #Add the type pattern bits to the code
            self.add_type_pattern(cur_mask, tables.type_bits[self.error][n])

            #Get the mask pattern
            pattern = tables.mask_patterns[n]

            #This will read the 1's and 0's one at a time
            bits = iter(self.buffer.getvalue())

            #These will help us do the up, down, up, down pattern
            row_start = itertools.cycle([len(cur_mask)-1, 0])
            row_stop = itertools.cycle([-1,len(cur_mask)])
            direction = itertools.cycle([-1, 1])

            #The data pattern is added using pairs of columns
            for column in range(len(cur_mask)-1, 0, -2):

                #The vertical timing pattern is an exception to the rules,
                #move the column counter over by one
                if column <= 6:
                    column = column - 1

                #This will let us fill in the pattern
                #right-left, right-left, etc.
                column_pair = itertools.cycle([column, column-1])

                #Go through each row in the pattern moving up, then down
                for row in range(next(row_start), next(row_stop),
                                 next(direction)):

                    #Fill in the right then left column
                    for i in range(2):
                        col = next(column_pair)

                        #Go to the next column if we encounter a
                        #preexisting pattern (usually an alignment pattern)
                        if cur_mask[row][col] != ' ':
                            continue

                        #Some versions don't have enough bits. You then fill
                        #in the rest of the pattern with 0's. These are
                        #called "remainder bits."
                        try:
                            bit = int(next(bits))
                        except:
                            bit = 0


                        #If the pattern is True then flip the bit
                        if pattern(row, col):
                            cur_mask[row][col] = bit ^ 1
                        else:
                            cur_mask[row][col] = bit

        #DEBUG CODE!!!
        #Save all of the masks as png files
        #for i, m in enumerate(masks):
        #    _png(m, self.version, 'mask-{0}.png'.format(i), 5)

        return masks

    def choose_best_mask(self):
        """This method returns the index of the "best" mask as defined by
        having the lowest total penalty score. The penalty rules are defined
        by the standard. The mask with the lowest total score should be the
        easiest to read by optical scanners.
        """
        self.scores = []
        for n in range(len(self.masks)):
            self.scores.append([0,0,0,0])

        #Score penalty rule number 1
        #Look for five consecutive squares with the same color.
        #Each one found gets a penalty of 3 + 1 for every
        #same color square after the first five in the row.
        for (n, mask) in enumerate(self.masks):
            current = mask[0][0]
            counter = 0
            total = 0

            #Examine the mask row wise
            for row in range(0,len(mask)):
                counter = 0
                for col  in range(0,len(mask)):
                    bit = mask[row][col]

                    if bit == current:
                        counter += 1
                    else:
                        if counter >= 5:
                            total += (counter - 5) + 3
                        counter = 1
                        current = bit
                if counter >= 5:
                    total += (counter - 5) + 3

            #Examine the mask column wise
            for col in range(0,len(mask)):
                counter = 0
                for row in range(0,len(mask)):
                    bit = mask[row][col]

                    if bit == current:
                        counter += 1
                    else:
                        if counter >= 5:
                            total += (counter - 5) + 3
                        counter = 1
                        current = bit
                if counter >= 5:
                    total += (counter - 5) + 3

            self.scores[n][0] = total

        #Score penalty rule 2
        #This rule will add 3 to the score for each 2x2 block of the same
        #colored pixels there are.
        for (n, mask) in enumerate(self.masks):
            count = 0
            #Don't examine the 0th and Nth row/column
            for i in range(0, len(mask)-1):
                for j in range(0, len(mask)-1):
                    if mask[i][j] == mask[i+1][j]   and \
                       mask[i][j] == mask[i][j+1]   and \
                       mask[i][j] == mask[i+1][j+1]:
                        count += 1

            self.scores[n][1] = count * 3

        #Score penalty rule 3
        #This rule looks for 1011101 within the mask prefixed
        #and/or suffixed by four zeros.
        patterns = [[0,0,0,0,1,0,1,1,1,0,1],
                    [1,0,1,1,1,0,1,0,0,0,0],]
                    #[0,0,0,0,1,0,1,1,1,0,1,0,0,0,0]]

        for (n, mask) in enumerate(self.masks):
            nmatches = 0

            for i in range(len(mask)):
                for j in range(len(mask)):
                    for pattern in patterns:
                        match = True
                        k = j
                        #Look for row matches
                        for p in pattern:
                            if k >= len(mask) or mask[i][k] != p:
                                match = False
                                break
                            k += 1
                        if match:
                            nmatches += 1

                        match = True
                        k = j
                        #Look for column matches
                        for p in pattern:
                            if k >= len(mask) or mask[k][i] != p:
                                match = False
                                break
                            k += 1
                        if match:
                            nmatches += 1


            self.scores[n][2] = nmatches * 40

        #Score the last rule, penalty rule 4. This rule measures how close
        #the pattern is to being 50% black. The further it deviates from
        #this this ideal the higher the penalty.
        for (n, mask) in enumerate(self.masks):
            nblack = 0
            for row in mask:
                nblack += sum(row)

            total_pixels = len(mask)**2
            ratio = nblack / total_pixels
            percent = (ratio * 100) - 50
            self.scores[n][3] = int((abs(int(percent)) / 5) * 10)


        #Calculate the total for each score
        totals = [0] * len(self.scores)
        for i in range(len(self.scores)):
            for j in range(len(self.scores[i])):
                totals[i] +=  self.scores[i][j]

        #DEBUG CODE!!!
        #Prints out a table of scores
        #print('Rule Scores\n      1     2     3     4    Total')
        #for i in range(len(self.scores)):
        #    print(i, end='')
        #    for s in self.scores[i]:
        #        print('{0: >6}'.format(s), end='')
        #    print('{0: >7}'.format(totals[i]))
        #print('Mask Chosen: {0}'.format(totals.index(min(totals))))

        #The lowest total wins
        return totals.index(min(totals))

    def add_type_pattern(self, m, type_bits):
        """This will add the pattern to the QR code that represents the error
        level and the type of mask used to make the code.
        """
        field = iter(type_bits)
        for i in range(7):
            bit = int(next(field))

            #Skip the timing bits
            if i < 6:
                m[8][i] = bit
            else:
                m[8][i+1] = bit

            if -8 < -(i+1):
                m[-(i+1)][8] = bit

        for i in range(-8,0):
            bit = int(next(field))

            m[8][i] = bit

            i = -i
            #Skip timing column
            if i > 6:
                m[i][8] = bit
            else:
                m[i-1][8] = bit

##############################################################################
##############################################################################
#
# Output Functions
#
##############################################################################
##############################################################################

def _get_writable(stream_or_path, mode):
    """This method returns a tuple containing the stream and a flag to indicate
    if the stream should be automatically closed.

    The `stream_or_path` parameter is returned if it is an open writable stream.
    Otherwise, it treats the `stream_or_path` parameter as a file path and
    opens it with the given mode.

    It is used by the svg and png methods to interpret the file parameter.

    :type stream_or_path: str | io.BufferedIOBase
    :type mode: str | unicode
    :rtype: (io.BufferedIOBase, bool)
    """
    is_stream = hasattr(stream_or_path, 'write')
    if not is_stream:
        # No stream provided, treat "stream_or_path" as path
        stream_or_path = open(stream_or_path, mode)
    return stream_or_path, not is_stream


def _get_png_size(version, scale, quiet_zone=4):
    """See: QRCode.get_png_size

    This function was abstracted away from QRCode to allow for the output of
    QR codes during the build process, i.e. for debugging. It works
    just the same except you must specify the code's version. This is needed
    to calculate the PNG's size.
    """
    #Formula: scale times number of modules plus the border on each side
    return (int(scale) * tables.version_size[version]) + (2 * quiet_zone * int(scale))


def _terminal(code, module_color='default', background='reverse', quiet_zone=4):
    """This method returns a string containing ASCII escape codes,
    such that if printed to a terminal, it will display a vaild
    QR code. The module_color and the background color should be keys
    in the tables.term_colors table for printing using the 8/16
    color scheme. Alternatively, they can be a number between 0 and
    256 in order to use the 88/256 color scheme. Otherwise, a
    ValueError will be raised.

    Note, the code is outputted by changing the background color. Then
    two spaces are written to the terminal. Finally, the terminal is
    reset back to how it was.
    """
    buf = io.StringIO()

    def draw_border():
        for i in range(quiet_zone):
            buf.write(background)

    if module_color in tables.term_colors:
        data = '\033[{0}m  \033[0m'.format(
            tables.term_colors[module_color])
    elif 0 <= module_color <= 256:
        data = '\033[48;5;{0}m  \033[0m'.format(module_color)
    else:
        raise ValueError('The module color, {0}, must a key in '
                         'pyqrcode.tables.term_colors or a number '
                         'between 0 and 256.'.format(
                         module_color))

    if background in tables.term_colors:
        background = '\033[{0}m  \033[0m'.format(
            tables.term_colors[background])
    elif 0 <= background <= 256:
        background = '\033[48;5;{0}m  \033[0m'.format(background)
    else:
        raise ValueError('The background color, {0}, must a key in '
                         'pyqrcode.tables.term_colors or a number '
                         'between 0 and 256.'.format(
                         background))

    #This will be the beginning and ending row for the code.
    border_row = background * (len(code[0]) + (2 * quiet_zone))

    #Make sure we begin on a new line, and force the terminal back
    #to normal
    buf.write('\n')

    #QRCodes have a quiet zone consisting of background modules
    for i in range(quiet_zone):
        buf.write(border_row)
        buf.write('\n')

    for row in code:
        #Each code has a quiet zone on the left side, this is the left
        #border for this code
        draw_border()

        for bit in row:
            if bit == 1:
                buf.write(data)
            elif bit == 0:
                buf.write(background)
        
        #Each row ends with a quiet zone on the right side, this is the
        #right hand border background modules
        draw_border()
        buf.write('\n')

    #QRCodes have a background quiet zone row following the code
    for i in range(quiet_zone):
        buf.write(border_row)
        buf.write('\n')

    return buf.getvalue()

def _text(code, quiet_zone=4):
    """This method returns a text based representation of the QR code.
    This is useful for debugging purposes.
    """
    buf = io.StringIO()

    border_row = '0' * (len(code[0]) + (quiet_zone*2))

    #Every QR code start with a quiet zone at the top
    for b in range(quiet_zone):
        buf.write(border_row)
        buf.write('\n')

    for row in code:
        #Draw the starting quiet zone
        for b in range(quiet_zone):
            buf.write('0')

        #Actually draw the QR code
        for bit in row:
            if bit == 1:
                buf.write('1')
            elif bit == 0:
                buf.write('0')
            #This is for debugging unfinished QR codes,
            #unset pixels will be spaces.
            else:
                buf.write(' ')
        
        #Draw the ending quiet zone
        for b in range(quiet_zone):
            buf.write('0')
        buf.write('\n')

    #Every QR code ends with a quiet zone at the bottom
    for b in range(quiet_zone):
        buf.write(border_row)
        buf.write('\n')

    return buf.getvalue()

def _xbm(code, scale=1, quiet_zone=4):
    """This function will format the QR code as a X BitMap.
    This can be used to display the QR code with Tkinter.
    """
    try:
        str = unicode  # Python 2
    except NameError:
        str = __builtins__['str']
        
    buf = io.StringIO()
    
    # Calculate the width in pixels
    pixel_width = (len(code[0]) + quiet_zone * 2) * scale
    
    # Add the size information and open the pixel data section
    buf.write('#define im_width ')
    buf.write(str(pixel_width))
    buf.write('\n')
    buf.write('#define im_height ')
    buf.write(str(pixel_width))
    buf.write('\n')
    buf.write('static char im_bits[] = {\n')
    
    # Calculate the number of bytes per row
    byte_width = int(math.ceil(pixel_width / 8.0))
    
    # Add the top quiet zone
    buf.write(('0x00,' * byte_width + '\n') * quiet_zone * scale)
    for row in code:
        # Add the left quiet zone
        row_bits = '0' * quiet_zone * scale
        # Add the actual QR code
        for pixel in row:
            row_bits += str(pixel) * scale
        # Add the right quiet zone
        row_bits += '0' * quiet_zone * scale
        # Format the row
        formated_row = ''
        for b in range(byte_width):
            formated_row += '0x{0:02x},'.format(int(row_bits[:8][::-1], 2))
            row_bits = row_bits[8:]
        formated_row += '\n'
        # Add the formatted row
        buf.write(formated_row * scale)
    # Add the bottom quiet zone and close the pixel data section
    buf.write(('0x00,' * byte_width + '\n') * quiet_zone * scale)
    buf.write('};')
    
    return buf.getvalue()

def _svg(code, version, file, scale=1, module_color='#000', background=None,
         quiet_zone=4, xmldecl=True, svgns=True, title=None, svgclass='pyqrcode',
         lineclass='pyqrline', omithw=False, debug=False):
    """This function writes the QR code out as an SVG document. The
    code is drawn by drawing only the modules corresponding to a 1. They
    are drawn using a line, such that contiguous modules in a row
    are drawn with a single line. The file parameter is used to
    specify where to write the document to. It can either be a writable (binary)
    stream or a file path. The scale parameter is sets how large to draw
    a single module. By default one pixel is used to draw a single
    module. This may make the code to small to be read efficiently.
    Increasing the scale will make the code larger. This method will accept
    fractional scales (e.g. 2.5).

    :param module_color: Color of the QR code (default: ``#000`` (black))
    :param background: Optional background color.
            (default: ``None`` (no background))
    :param quiet_zone: Border around the QR code (also known as  quiet zone)
            (default: ``4``). Set to zero (``0``) if the code shouldn't
            have a border.
    :param xmldecl: Inidcates if the XML declaration header should be written
            (default: ``True``)
    :param svgns: Indicates if the SVG namespace should be written
            (default: ``True``)
    :param title: Optional title of the generated SVG document.
    :param svgclass: The CSS class of the SVG document
            (if set to ``None``, the SVG element won't have a class).
    :param lineclass: The CSS class of the path element
            (if set to ``None``, the path won't have a class).
    :param omithw: Indicates if width and height attributes should be
            omitted (default: ``False``). If these attributes are omitted,
            a ``viewBox`` attribute will be added to the document.
    :param debug: Inidicates if errors in the QR code should be added to the
            output (default: ``False``).
    """
    from functools import partial
    from xml.sax.saxutils import quoteattr

    def write_unicode(write_meth, unicode_str):
        """\
        Encodes the provided string into UTF-8 and writes the result using
        the `write_meth`.
        """
        write_meth(unicode_str.encode('utf-8'))

    def line(x, y, length, relative):
        """Returns coordinates to draw a line with the provided length.
        """
        return '{0}{1} {2}h{3}'.format(('m' if relative else 'M'), x, y, length)

    def errline(col_number, row_number):
        """Returns the coordinates to draw an error bit.
        """
        # Debug path uses always absolute coordinates
        # .5 == stroke / 2
        return line(col_number + quiet_zone, row_number + quiet_zone + .5, 1, False)

    f, autoclose = _get_writable(file, 'wb')
    write = partial(write_unicode, f.write)
    write_bytes = f.write
    # Write the document header
    if xmldecl:
        write_bytes(b'<?xml version="1.0" encoding="UTF-8"?>\n')
    write_bytes(b'<svg')
    if svgns:
        write_bytes(b' xmlns="http://www.w3.org/2000/svg"')
    size = tables.version_size[version] * scale + (2 * quiet_zone * scale)
    if not omithw:
        write(' height="{0}" width="{0}"'.format(size))
    else:
        write(' viewBox="0 0 {0} {0}"'.format(size))
    if svgclass is not None:
        write_bytes(b' class=')
        write(quoteattr(svgclass))
    write_bytes(b'>')
    if title is not None:
        write('<title>{0}</title>'.format(title))

    # Draw a background rectangle if necessary
    if background is not None:
        write('<path fill="{1}" d="M0 0h{0}v{0}h-{0}z"/>'
                .format(size, background))
    write_bytes(b'<path')
    if scale != 1:
        write(' transform="scale({0})"'.format(scale))
    if module_color is not None:
        write_bytes(b' stroke=')
        write(quoteattr(module_color))
    if lineclass is not None:
        write_bytes(b' class=')
        write(quoteattr(lineclass))
    write_bytes(b' d="')
    # Used to keep track of unknown/error coordinates.
    debug_path = ''
    # Current pen pointer position
    x, y = -quiet_zone, quiet_zone - .5  # .5 == stroke-width / 2
    wrote_bit = False
    # Loop through each row of the code
    for rnumber, row in enumerate(code):
        start_column = 0  # Reset the starting column number
        coord = ''  # Reset row coordinates
        y += 1  # Pen position on y-axis
        length = 0  # Reset line length
        # Examine every bit in the row
        for colnumber, bit in enumerate(row):
            if bit == 1:
                length += 1
            else:
                if length:
                    x = start_column - x
                    coord += line(x, y, length, relative=wrote_bit)
                    x = start_column + length
                    y = 0  # y-axis won't change unless the row changes
                    length = 0
                    wrote_bit = True
                start_column = colnumber + 1
                if debug and bit != 0:
                    debug_path += errline(colnumber, rnumber)
        if length:
            x = start_column - x
            coord += line(x, y, length, relative=wrote_bit)
            x = start_column + length
            wrote_bit = True
        write(coord)
    # Close path
    write_bytes(b'"/>')
    if debug and debug_path:
        write_bytes(b'<path')
        if scale != 1:
            write(' transform="scale({0})"'.format(scale))
        write(' class="pyqrerr" stroke="red" d="{0}"/>'.format(debug_path))
    # Close document
    write_bytes(b'</svg>\n')
    if autoclose:
        f.close()


def _png(code, version, file, scale=1, module_color=(0, 0, 0, 255),
         background=(255, 255, 255, 255), quiet_zone=4, debug=False):
    """See: pyqrcode.QRCode.png()

    This function was abstracted away from QRCode to allow for the output of
    QR codes during the build process, i.e. for debugging. It works
    just the same except you must specify the code's version. This is needed
    to calculate the PNG's size.

    This method will write the given file out as a PNG file. Note, it
    depends on the PyPNG module to do this.

    :param module_color: Color of the QR code (default: ``(0, 0, 0, 255)`` (black))
    :param background: Optional background color. If set to ``None`` the PNG
            will have a transparent background.
            (default: ``(255, 255, 255, 255)`` (white))
    :param quiet_zone: Border around the QR code (also known as quiet zone)
            (default: ``4``). Set to zero (``0``) if the code shouldn't
            have a border.
    :param debug: Inidicates if errors in the QR code should be added (as red
            modules) to the output (default: ``False``).
    """
    import png
    
    # Coerce scale parameter into an integer
    try:
        scale = int(scale)
    except ValueError:
        raise ValueError('The scale parameter must be an integer')

    def scale_code(size):
        """To perform the scaling we need to inflate the number of bits.
        The PNG library expects all of the bits when it draws the PNG.
        Effectively, we double, tripple, etc. the number of columns and
        the number of rows.
        """
        # This is one row's worth of each possible module
        # PNG's use 0 for black and 1 for white, this is the
        # reverse of the QR standard
        black = [0] * scale
        white = [1] * scale

        # Tuple to lookup colors
        # The 3rd color is the module_color unless "debug" is enabled
        colors = (white, black, (([2] * scale) if debug else black))

        # Whitespace added on the left and right side
        border_module = white * quiet_zone
        # This is the row to show up at the top and bottom border
        border_row = [[1] * size] * scale * quiet_zone

        # This will hold the final PNG's bits
        bits = []

        # Add scale rows before the code as a border,
        # as per the standard
        bits.extend(border_row)

        # Add each row of the to the final PNG bits
        for row in code:
            tmp_row = []

            # Add one all white module to the beginning
            # to create the vertical border
            tmp_row.extend(border_module)

            # Go through each bit in the code
            for bit in row:
                # Use the standard color or the "debug" color
                tmp_row.extend(colors[(bit if bit in (0, 1) else 2)])

            # Add one all white module to the end
            # to create the vertical border
            tmp_row.extend(border_module)

            # Copy each row scale times
            for n in range(scale):
                bits.append(tmp_row)

        # Add the bottom border
        bits.extend(border_row)

        return bits

    def png_pallete_color(color):
        """This creates a palette color from a list or tuple. The list or
        tuple must be of length 3 (for rgb) or 4 (for rgba). The values
        must be between 0 and 255. Note rgb colors will be given an added
        alpha component set to 255.

        The pallete color is represented as a list, this is what is returned.
        """
        if color is None:
            return ()
        if not isinstance(color, (tuple, list)):
            r, g, b = _hex_to_rgb(color)
            return r, g, b, 255
        rgba = []
        if not (3 <= len(color) <= 4):
            raise ValueError('Colors must be a list or tuple of length '
                             ' 3 or 4. You passed in "{0}".'.format(color))
        for c in color:
            c = int(c)
            if 0 <= c <= 255:
                rgba.append(int(c))
            else:
                raise ValueError('Color components must be between 0 and 255')
        # Make all colors have an alpha channel
        if len(rgba) == 3:
            rgba.append(255)
        return tuple(rgba)

    if module_color is None:
        raise ValueError('The module_color must not be None')

    bitdepth = 1
    # foreground aka module color
    fg_col = png_pallete_color(module_color)
    transparent = background is None
    # If background color is set to None, the inverse color of the
    # foreground color is calculated
    bg_col = png_pallete_color(background) if background is not None else tuple([255 - c for c in fg_col])
    # Assume greyscale if module color is black and background color is white
    greyscale = fg_col[:3] == (0, 0, 0) and (not debug and transparent or bg_col == (255, 255, 255, 255))
    transparent_color = 1 if transparent and greyscale else None
    palette = [fg_col, bg_col] if not greyscale else None
    if debug:
        # Add "red" as color for error modules
        palette.append((255, 0, 0, 255))
        bitdepth = 2

    # The size of the PNG
    size = _get_png_size(version, scale, quiet_zone)

    # We need to increase the size of the code to match up to the
    # scale parameter.
    code_rows = scale_code(size)

    # Write out the PNG
    f, autoclose = _get_writable(file, 'wb')
    w = png.Writer(width=size, height=size, greyscale=greyscale,
                   transparent=transparent_color, palette=palette,
                   bitdepth=bitdepth)
    try:
        w.write(f, code_rows)
    finally:
        if autoclose:
            f.close()


def _eps(code, version, file_or_path, scale=1, module_color=(0, 0, 0),
         background=None, quiet_zone=4):
    """This function writes the QR code out as an EPS document. The
    code is drawn by drawing only the modules corresponding to a 1. They
    are drawn using a line, such that contiguous modules in a row
    are drawn with a single line. The file parameter is used to
    specify where to write the document to. It can either be a writable (text)
    stream or a file path. The scale parameter is sets how large to draw
    a single module. By default one point (1/72 inch) is used to draw a single
    module. This may make the code to small to be read efficiently.
    Increasing the scale will make the code larger. This function will accept
    fractional scales (e.g. 2.5).

    :param module_color: Color of the QR code (default: ``(0, 0, 0)`` (black))
            The color can be specified as triple of floats (range: 0 .. 1) or
            triple of integers (range: 0 .. 255) or as hexadecimal value (i.e.
            ``#36c`` or ``#33B200``).
    :param background: Optional background color.
            (default: ``None`` (no background)). See `module_color` for the
            supported values.
    :param quiet_zone: Border around the QR code (also known as  quiet zone)
            (default: ``4``). Set to zero (``0``) if the code shouldn't
            have a border.
    """
    from functools import partial
    import time
    import textwrap

    def write_line(writemeth, content):
        """\
        Writes `content` and ``LF``.
        """
        # Postscript: Max. 255 characters per line
        for line in textwrap.wrap(content, 255):
            writemeth(line)
            writemeth('\n')

    def line(offset, length):
        """\
        Returns coordinates to draw a line with the provided length.
        """
        res = ''
        if offset > 0:
            res = ' {0} 0 m'.format(offset)
        res += ' {0} 0 l'.format(length)
        return res

    def rgb_to_floats(color):
        """\
        Converts the provided color into an acceptable format for Postscript's
         ``setrgbcolor``
        """
        def to_float(clr):
            if isinstance(clr, float):
                if not 0.0 <= clr <= 1.0:
                    raise ValueError('Invalid color "{0}". Not in range 0 .. 1'
                                     .format(clr))
                return clr
            if not 0 <= clr <= 255:
                raise ValueError('Invalid color "{0}". Not in range 0 .. 255'
                                 .format(clr))
            return 1/255.0 * clr if clr != 1 else clr

        if not isinstance(color, (tuple, list)):
            color = _hex_to_rgb(color)
        return tuple([to_float(i) for i in color])

    f, autoclose = _get_writable(file_or_path, 'w')
    writeline = partial(write_line, f.write)
    size = tables.version_size[version] * scale + (2 * quiet_zone * scale)
    # Write common header
    writeline('%!PS-Adobe-3.0 EPSF-3.0')
    writeline('%%Creator: PyQRCode <https://pypi.python.org/pypi/PyQRCode/>')
    writeline('%%CreationDate: {0}'.format(time.strftime("%Y-%m-%d %H:%M:%S")))
    writeline('%%DocumentData: Clean7Bit')
    writeline('%%BoundingBox: 0 0 {0} {0}'.format(size))
    # Write the shortcuts
    writeline('/M { moveto } bind def')
    writeline('/m { rmoveto } bind def')
    writeline('/l { rlineto } bind def')
    mod_color = module_color if module_color == (0, 0, 0) else rgb_to_floats(module_color)
    if background is not None:
        writeline('{0:f} {1:f} {2:f} setrgbcolor clippath fill'
                  .format(*rgb_to_floats(background)))
        if mod_color == (0, 0, 0):
            # Reset RGB color back to black iff module color is black
            # In case module color != black set the module RGB color later
            writeline('0 0 0 setrgbcolor')
    if mod_color != (0, 0, 0):
        writeline('{0:f} {1:f} {2:f} setrgbcolor'.format(*mod_color))
    if scale != 1:
        writeline('{0} {0} scale'.format(scale))
    writeline('newpath')
    # Current pen position y-axis
    # Note: 0, 0 = lower left corner in PS coordinate system
    y = tables.version_size[version] + quiet_zone + .5  # .5 = linewidth / 2
    last_bit = 1
    # Loop through each row of the code
    for row in code:
        offset = 0  # Set x-offset of the pen
        length = 0
        y -= 1  # Move pen along y-axis
        coord = '{0} {1} M'.format(quiet_zone, y)  # Move pen to initial pos
        for bit in row:
            if bit != last_bit:
                if length:
                    coord += line(offset, length)
                    offset = 0
                    length = 0
                last_bit = bit
            if bit == 1:
                length += 1
            else:
                offset += 1
        if length:
            coord += line(offset, length)
        writeline(coord)
    writeline('stroke')
    writeline('%%EOF')
    if autoclose:
        f.close()


def _hex_to_rgb(color):
    """\
    Helper function to convert a color provided in hexadecimal format
    as RGB triple.
    """
    if color[0] == '#':
        color = color[1:]
    if len(color) == 3:
        color = color[0] * 2 + color[1] * 2 + color[2] * 2
    if len(color) != 6:
        raise ValueError('Input #{0} is not in #RRGGBB format'.format(color))
    return [int(n, 16) for n in (color[:2], color[2:4], color[4:])]