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# A general recursive descent parser
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import re
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class SyntaxException(Exception): pass
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class Parser:
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def __init__(self, string):
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self._str = string
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self._pos = 0
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def parse(self):
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tree = self._main()
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if not self._pos == len(self._str): self._syntax_err('End of string')
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return tree
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def _match_re(self, pattern, required=False):
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matcher = re.compile(pattern).match(self._str, self._pos)
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if matcher:
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self._pos = matcher.end(0)
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return matcher.group(0)
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elif required: self._syntax_err(pattern)
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else: return None
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def _match_str(self, string, required=False):
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end_pos = self._pos + len(string)
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if self._str[self._pos:end_pos] == string:
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self._pos = end_pos
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return True
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elif required: self._syntax_err(string)
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else: return False
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def _syntax_err(self, token):
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raise SyntaxException(self.__class__.__name__+' syntax error: '+token
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+' expected in '+self._str[self._pos:])
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