148 lines
3.9 KiB
Python
148 lines
3.9 KiB
Python
# Regular expression subroutines:
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# sub(pat, repl, str): replace first occurrence of pattern in string
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# gsub(pat, repl, str): replace all occurrences of pattern in string
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# split(str, pat): split string using pattern as delimiter
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import regex
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# Replace first occurrence of pattern pat in string str by replacement
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# repl. If the pattern isn't found, the string is returned unchanged.
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# The replacement may contain references \digit to subpatterns and
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# escaped backslashes. The pattern may be a string or an already
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# compiled pattern.
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def sub(pat, repl, str):
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prog = compile(pat)
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if prog.search(str) >= 0:
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regs = prog.regs
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a, b = regs[0]
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str = str[:a] + expand(repl, regs, str) + str[b:]
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return str
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# Replace all (non-overlapping) occurrences of pattern pat in string
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# str by replacement repl. The same rules as for sub() apply.
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# Empty matches for the pattern are replaced only when not adjacent to
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# a previous match, so e.g. gsub('', '-', 'abc') returns '-a-b-c-'.
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def gsub(pat, repl, str):
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prog = compile(pat)
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new = ''
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start = 0
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first = 1
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while prog.search(str, start) >= 0:
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regs = prog.regs
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a, b = regs[0]
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if a == b == start and not first:
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if start >= len(str) or prog.search(str, start+1) < 0:
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break
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regs = prog.regs
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a, b = regs[0]
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new = new + str[start:a] + expand(repl, regs, str)
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start = b
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first = 0
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new = new + str[start:]
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return new
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# Split string str in fields separated by delimiters matching pattern
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# pat. Only non-empty matches for the pattern are considered, so e.g.
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# split('abc', '') returns ['abc'].
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def split(str, pat):
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prog = compile(pat)
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res = []
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start = next = 0
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while prog.search(str, next) >= 0:
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regs = prog.regs
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a, b = regs[0]
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if a == b:
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next = next + 1
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if next >= len(str):
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break
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else:
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res.append(str[start:a])
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start = next = b
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res.append(str[start:])
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return res
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# Internal subroutines:
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# compile(pat): compile a pattern, caching already compiled patterns
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# expand(repl, regs, str): expand \digit escapes in replacement string
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# Manage a cache of compiled regular expressions.
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# If the pattern is a string a compiled version of it is returned.
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# If the pattern has been used before we return an already compiled
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# version from the cache; otherwise we compile it now and save the
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# compiled version in the cache.
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# Instead of a string, a compiled regular expression can also be
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# passed.
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# WARNING: if the pattern syntax is changed, the cache should be
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# flushed!
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cache = {}
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def compile(pat):
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if type(pat) <> type(''):
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return pat # Assume it is a compiled regex
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if cache.has_key(pat):
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prog = cache[pat] # Get it from the cache
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else:
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prog = cache[pat] = regex.compile(pat)
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return prog
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# Expand \digit in the replacement.
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# Each occurrence of \digit is replaced by the substring of str
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# indicated by regs[digit]. To include a literal \ in the
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# replacement, double it; other \ escapes are left unchanged (i.e.
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# the \ and the following character are both copied).
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def expand(repl, regs, str):
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if '\\' not in repl:
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return repl
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new = ''
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i = 0
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while i < len(repl):
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c = repl[i]; i = i+1
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if c <> '\\' or i >= len(repl):
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new = new + c
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else:
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c = repl[i]; i = i+1
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if '0' <= c <= '9':
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a, b = regs[eval(c)]
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new = new + str[a:b]
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elif c == '\\':
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new = new + c
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else:
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new = new + '\\' + c
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return new
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# Test program, reads sequences "pat repl str" from stdin.
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# Optional argument specifies pattern used to split lines.
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def test():
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import sys
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if sys.argv[1:]:
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delpat = sys.argv[1]
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else:
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delpat = '[ \t\n]+'
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while 1:
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if sys.stdin.isatty(): sys.stderr.write('--> ')
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line = sys.stdin.readline()
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if not line: break
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if line[-1] == '\n': line = line[:-1]
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fields = split(line, delpat)
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if len(fields) <> 3:
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print 'Sorry, not three fields'
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print 'split:', `fields`
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continue
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[pat, repl, str] = split(line, delpat)
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print 'sub :', `sub(pat, repl, str)`
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print 'gsub:', `gsub(pat, repl, str)`
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