UPC: Difference between revisions
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</pre> |
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=={{header|Python}}== |
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<lang python>"""UPC-A barcode reader. Requires Python =>3.6""" |
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import itertools |
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import re |
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RE_BARCODE = re.compile( |
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r"^(?P<s_quiet> +)" # quiet zone |
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r"(?P<s_guard># #)" # start guard |
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r"(?P<left>[ #]{42})" # left digits |
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r"(?P<m_guard> # # )" # middle guard |
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r"(?P<right>[ #]{42})" # right digits |
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r"(?P<e_guard># #)" # end guard |
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r"(?P<e_quiet> +)$" # quiet zone |
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) |
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LEFT_DIGITS = { |
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(0, 0, 0, 1, 1, 0, 1): 0, |
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(0, 0, 1, 1, 0, 0, 1): 1, |
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(0, 0, 1, 0, 0, 1, 1): 2, |
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(0, 1, 1, 1, 1, 0, 1): 3, |
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(0, 1, 0, 0, 0, 1, 1): 4, |
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(0, 1, 1, 0, 0, 0, 1): 5, |
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(0, 1, 0, 1, 1, 1, 1): 6, |
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(0, 1, 1, 1, 0, 1, 1): 7, |
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(0, 1, 1, 0, 1, 1, 1): 8, |
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(0, 0, 0, 1, 0, 1, 1): 9, |
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} |
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RIGHT_DIGITS = { |
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(1, 1, 1, 0, 0, 1, 0): 0, |
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(1, 1, 0, 0, 1, 1, 0): 1, |
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(1, 1, 0, 1, 1, 0, 0): 2, |
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(1, 0, 0, 0, 0, 1, 0): 3, |
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(1, 0, 1, 1, 1, 0, 0): 4, |
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(1, 0, 0, 1, 1, 1, 0): 5, |
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(1, 0, 1, 0, 0, 0, 0): 6, |
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(1, 0, 0, 0, 1, 0, 0): 7, |
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(1, 0, 0, 1, 0, 0, 0): 8, |
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(1, 1, 1, 0, 1, 0, 0): 9, |
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} |
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MODULES = { |
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" ": 0, |
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"#": 1, |
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} |
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DIGITS_PER_SIDE = 6 |
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MODULES_PER_DIGIT = 7 |
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class ParityError(Exception): |
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"""Exception raised when a parity error is found.""" |
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class ChecksumError(Exception): |
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"""Exception raised when check digit does not match.""" |
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def group(iterable, n): |
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"""Chunk the iterable into groups of size ``n``.""" |
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args = [iter(iterable)] * n |
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return tuple(itertools.zip_longest(*args)) |
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def parse(barcode): |
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"""Return the 12 digits represented by the given barcode. Raises a |
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ParityError if any digit fails the parity check.""" |
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match = RE_BARCODE.match(barcode) |
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# Translate bars and spaces to 1s and 0s so we can do arithmetic |
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# with them. Group "modules" into chunks of 7 as we go. |
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left = group((MODULES[c] for c in match.group("left")), MODULES_PER_DIGIT) |
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right = group((MODULES[c] for c in match.group("right")), MODULES_PER_DIGIT) |
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# Parity check |
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left, right = check_parity(left, right) |
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# Lookup digits |
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return tuple( |
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itertools.chain( |
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(LEFT_DIGITS[d] for d in left), |
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(RIGHT_DIGITS[d] for d in right), |
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) |
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) |
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def check_parity(left, right): |
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"""Check left and right parity. Flip left and right if the barcode |
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was scanned upside down.""" |
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# When reading from left to right, each digit on the left should |
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# have odd parity, and each digit on the right should have even |
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# parity. |
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left_parity = sum(sum(d) % 2 for d in left) |
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right_parity = sum(sum(d) % 2 for d in right) |
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# Use left and right parity to check if the barcode was scanned |
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# upside down. Flip it if it was. |
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if left_parity == 0 and right_parity == DIGITS_PER_SIDE: |
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_left = tuple(tuple(reversed(d)) for d in reversed(right)) |
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right = tuple(tuple(reversed(d)) for d in reversed(left)) |
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left = _left |
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elif left_parity != DIGITS_PER_SIDE or right_parity != 0: |
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# Error condition. Mixed parity. |
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error = tuple( |
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itertools.chain( |
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(LEFT_DIGITS.get(d, "_") for d in left), |
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(RIGHT_DIGITS.get(d, "_") for d in right), |
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) |
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) |
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raise ParityError(" ".join(str(d) for d in error)) |
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return left, right |
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def checksum(digits): |
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"""Return the check digit for the given digits. Raises a |
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ChecksumError if the check digit does not match.""" |
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odds = (digits[i] for i in range(0, 11, 2)) |
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evens = (digits[i] for i in range(1, 10, 2)) |
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check_digit = (sum(odds) * 3 + sum(evens)) % 10 |
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if check_digit != 0: |
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check_digit = 10 - check_digit |
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if digits[-1] != check_digit: |
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raise ChecksumError(str(check_digit)) |
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return check_digit |
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def main(): |
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barcodes = [ |
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" # # # ## # ## # ## ### ## ### ## #### # # # ## ## # # ## ## ### # ## ## ### # # # ", |
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" # # # ## ## # #### # # ## # ## # ## # # # ### # ### ## ## ### # # ### ### # # # ", |
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" # # # # # ### # # # # # # # # # # ## # ## # ## # ## # # #### ### ## # # ", |
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" # # ## ## ## ## # # # # ### # ## ## # # # ## ## # ### ## ## # # #### ## # # # ", |
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" # # ### ## # ## ## ### ## # ## # # ## # # ### # ## ## # # ### # ## ## # # # ", |
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" # # # # ## ## # # # # ## ## # # # # # #### # ## # #### #### # # ## # #### # # ", |
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" # # # ## ## # # ## ## # ### ## ## # # # # # # # # ### # # ### # # # # # ", |
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" # # # # ## ## # # ## ## ### # # # # # ### ## ## ### ## ### ### ## # ## ### ## # # ", |
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" # # ### ## ## # # #### # ## # #### # #### # # # # # ### # # ### # # # ### # # # ", |
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" # # # #### ## # #### # # ## ## ### #### # # # # ### # ### ### # # ### # # # ### # # ", |
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" # # # #### ## # #### # # ## ## ### #### # # # # ### # ### ### # # ### ## ## # ### # # ", |
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] |
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for barcode in barcodes: |
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try: |
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digits = parse(barcode) |
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except ParityError as err: |
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print(f"{err} parity error!") |
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continue |
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try: |
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check_digit = checksum(digits) |
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except ChecksumError as err: |
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print(f"{' '.join(str(d) for d in digits)} checksum error! ({err})") |
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continue |
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print(f"{' '.join(str(d) for d in digits)}") |
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if __name__ == "__main__": |
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main() |
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</lang> |
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{{out}} |
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<pre> |
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$ python barcode.py |
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9 2 4 7 7 3 2 7 1 0 1 9 |
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4 0 3 9 4 4 4 4 1 0 5 0 |
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8 3 4 9 9 9 6 7 6 7 0 6 |
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9 3 9 8 2 5 1 5 8 8 1 1 |
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7 4 8 1 5 9 9 2 3 9 2 _ parity error! |
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3 1 6 3 1 3 7 1 8 7 1 7 |
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2 1 4 5 7 5 8 7 5 6 0 8 |
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8 1 8 7 7 8 8 4 1 8 1 3 |
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7 0 6 4 6 6 7 4 3 0 3 0 |
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6 5 3 4 8 3 5 4 0 4 3 5 |
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6 5 3 4 8 3 5 4 0 4 2 5 checksum error! (8) |
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</pre> |
</pre> |
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