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Python FEN chess Validation with regular expression
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def fenPass(fen): | |
""" | |
""" | |
regexMatch=re.match('\s*^(((?:[rnbqkpRNBQKP1-8]+\/){7})[rnbqkpRNBQKP1-8]+)\s([b|w])\s([K|Q|k|q]{1,4})\s(-|[a-h][1-8])\s(\d+\s\d+)$', fen) | |
if regexMatch: | |
regexList = regexMatch.groups() | |
fen = regexList[0].split("/") | |
if len(fen) != 8: | |
raise ValueError("expected 8 rows in position part of fen: {0}".format(repr(fen))) | |
for fenPart in fen: | |
field_sum = 0 | |
previous_was_digit, previous_was_piece = False,False | |
for c in fenPart: | |
if c in ["1", "2", "3", "4", "5", "6", "7", "8"]: | |
if previous_was_digit: | |
raise ValueError("two subsequent digits in position part of fen: {0}".format(repr(fen))) | |
field_sum += int(c) | |
previous_was_digit = True | |
previous_was_piece = False | |
elif c == "~": | |
if not previous_was_piece: | |
raise ValueError("~ not after piece in position part of fen: {0}".format(repr(fen))) | |
previous_was_digit, previous_was_piece = False,False | |
elif c.lower() in ["p", "n", "b", "r", "q", "k"]: | |
field_sum += 1 | |
previous_was_digit = False | |
previous_was_piece = True | |
else: | |
raise ValueError("invalid character in position part of fen: {0}".format(repr(fen))) | |
if field_sum != 8: | |
raise ValueError("expected 8 columns per row in position part of fen: {0}".format(repr(fen))) | |
else: raise ValueError("fen doesn`t match follow this example: rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1 ") | |
def main(): | |
try: | |
fenPass('rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1') | |
except ValueError as e: | |
print e.message | |
if __name__ == '__main__': | |
main() |
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For regexList = regexMatch.groups(), it may be better to replace this with regexList = fen.split().
For this FEN: "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1", regexMatch.groups() incorrectly set regexList equal to:
["rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR", "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/", "w", "KQkq", "-", "0 1"]
The second element shouldn't exist ("w" should be there), and the "0" and "1" should be the 5th and 6th elements instead of being together.