159 lines
4 KiB
Python
159 lines
4 KiB
Python
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#=======================================================================
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#
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# Python Lexical Analyser
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#
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# Traditional Regular Expression Syntax
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#
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#=======================================================================
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from __future__ import absolute_import
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from .Regexps import Alt, Seq, Rep, Rep1, Opt, Any, AnyBut, Bol, Eol, Char
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from .Errors import PlexError
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class RegexpSyntaxError(PlexError):
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pass
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def re(s):
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"""
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Convert traditional string representation of regular expression |s|
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into Plex representation.
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"""
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return REParser(s).parse_re()
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class REParser(object):
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def __init__(self, s):
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self.s = s
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self.i = -1
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self.end = 0
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self.next()
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def parse_re(self):
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re = self.parse_alt()
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if not self.end:
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self.error("Unexpected %s" % repr(self.c))
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return re
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def parse_alt(self):
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"""Parse a set of alternative regexps."""
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re = self.parse_seq()
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if self.c == '|':
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re_list = [re]
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while self.c == '|':
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self.next()
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re_list.append(self.parse_seq())
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re = Alt(*re_list)
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return re
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def parse_seq(self):
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"""Parse a sequence of regexps."""
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re_list = []
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while not self.end and not self.c in "|)":
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re_list.append(self.parse_mod())
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return Seq(*re_list)
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def parse_mod(self):
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"""Parse a primitive regexp followed by *, +, ? modifiers."""
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re = self.parse_prim()
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while not self.end and self.c in "*+?":
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if self.c == '*':
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re = Rep(re)
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elif self.c == '+':
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re = Rep1(re)
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else: # self.c == '?'
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re = Opt(re)
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self.next()
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return re
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def parse_prim(self):
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"""Parse a primitive regexp."""
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c = self.get()
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if c == '.':
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re = AnyBut("\n")
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elif c == '^':
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re = Bol
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elif c == '$':
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re = Eol
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elif c == '(':
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re = self.parse_alt()
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self.expect(')')
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elif c == '[':
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re = self.parse_charset()
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self.expect(']')
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else:
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if c == '\\':
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c = self.get()
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re = Char(c)
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return re
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def parse_charset(self):
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"""Parse a charset. Does not include the surrounding []."""
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char_list = []
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invert = 0
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if self.c == '^':
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invert = 1
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self.next()
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if self.c == ']':
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char_list.append(']')
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self.next()
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while not self.end and self.c != ']':
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c1 = self.get()
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if self.c == '-' and self.lookahead(1) != ']':
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self.next()
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c2 = self.get()
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for a in range(ord(c1), ord(c2) + 1):
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char_list.append(chr(a))
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else:
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char_list.append(c1)
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chars = ''.join(char_list)
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if invert:
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return AnyBut(chars)
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else:
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return Any(chars)
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def next(self):
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"""Advance to the next char."""
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s = self.s
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i = self.i = self.i + 1
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if i < len(s):
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self.c = s[i]
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else:
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self.c = ''
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self.end = 1
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def get(self):
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if self.end:
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self.error("Premature end of string")
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c = self.c
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self.next()
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return c
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def lookahead(self, n):
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"""Look ahead n chars."""
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j = self.i + n
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if j < len(self.s):
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return self.s[j]
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else:
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return ''
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def expect(self, c):
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"""
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Expect to find character |c| at current position.
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Raises an exception otherwise.
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"""
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if self.c == c:
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self.next()
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else:
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self.error("Missing %s" % repr(c))
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def error(self, mess):
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"""Raise exception to signal syntax error in regexp."""
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raise RegexpSyntaxError("Syntax error in regexp %s at position %d: %s" % (
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repr(self.s), self.i, mess))
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