EuroCD 3/EuroCD 3.iso/Programming/Python-1.4/Lib/regsub.py

Text File | 1998-06-24 | 5KB | 183 lines

# Regular expression subroutines:
# sub(pat, repl, str): replace first occurrence of pattern in string
# gsub(pat, repl, str): replace all occurrences of pattern in string
# split(str, pat, maxsplit): split string using pattern as delimiter
# splitx(str, pat, maxsplit): split string using pattern as delimiter plus
#                  return delimiters


import regex


# Replace first occurrence of pattern pat in string str by replacement
# repl.  If the pattern isn't found, the string is returned unchanged.
# The replacement may contain references \digit to subpatterns and
# escaped backslashes.  The pattern may be a string or an already
# compiled pattern.

def sub(pat, repl, str):
    prog = compile(pat)
    if prog.search(str) >= 0:
        regs = prog.regs
        a, b = regs[0]
        str = str[:a] + expand(repl, regs, str) + str[b:]
    return str


# Replace all (non-overlapping) occurrences of pattern pat in string
# str by replacement repl.  The same rules as for sub() apply.
# Empty matches for the pattern are replaced only when not adjacent to
# a previous match, so e.g. gsub('', '-', 'abc') returns '-a-b-c-'.

def gsub(pat, repl, str):
    prog = compile(pat)
    new = ''
    start = 0
    first = 1
    while prog.search(str, start) >= 0:
        regs = prog.regs
        a, b = regs[0]
        if a == b == start and not first:
            if start >= len(str) or prog.search(str, start+1) < 0:
                break
            regs = prog.regs
            a, b = regs[0]
        new = new + str[start:a] + expand(repl, regs, str)
        start = b
        first = 0
    new = new + str[start:]
    return new


# Split string str in fields separated by delimiters matching pattern
# pat.  Only non-empty matches for the pattern are considered, so e.g.
# split('abc', '') returns ['abc'].
# The optional 3rd argument sets the number of splits that are performed.

def split(str, pat, maxsplit = 0):
    return intsplit(str, pat, maxsplit, 0)

# Split string str in fields separated by delimiters matching pattern
# pat.  Only non-empty matches for the pattern are considered, so e.g.
# split('abc', '') returns ['abc']. The delimiters are also included
# in the list.
# The optional 3rd argument sets the number of splits that are performed.


def splitx(str, pat, maxsplit = 0):
    return intsplit(str, pat, maxsplit, 1)

# Internal function used to implement split() and splitx().

def intsplit(str, pat, maxsplit, retain):
    prog = compile(pat)
    res = []
    start = next = 0
    splitcount = 0
    while prog.search(str, next) >= 0:
        regs = prog.regs
        a, b = regs[0]
        if a == b:
            next = next + 1
            if next >= len(str):
                break
        else:
            res.append(str[start:a])
            if retain:
                res.append(str[a:b])
            start = next = b
            splitcount = splitcount + 1
            if (maxsplit and (splitcount >= maxsplit)):
                break
    res.append(str[start:])
    return res


# Capitalize words split using a pattern

def capwords(str, pat='[^a-zA-Z0-9_]+'):
    import string
    words = splitx(str, pat)
    for i in range(0, len(words), 2):
        words[i] = string.capitalize(words[i])
    return string.joinfields(words, "")


# Internal subroutines:
# compile(pat): compile a pattern, caching already compiled patterns
# expand(repl, regs, str): expand \digit escapes in replacement string


# Manage a cache of compiled regular expressions.
# If the pattern is a string a compiled version of it is returned.
# If the pattern has been used before we return an already compiled
# version from the cache; otherwise we compile it now and save the
# compiled version in the cache.
# Instead of a string, a compiled regular expression can also be
# passed.
# WARNING: if the pattern syntax is changed, the cache should be
# flushed!

cache = {}

def compile(pat):
    if type(pat) <> type(''):
        return pat        # Assume it is a compiled regex
    if cache.has_key(pat):
        prog = cache[pat]    # Get it from the cache
    else:
        prog = cache[pat] = regex.compile(pat)
    return prog


# Expand \digit in the replacement.
# Each occurrence of \digit is replaced by the substring of str
# indicated by regs[digit].  To include a literal \ in the
# replacement, double it; other \ escapes are left unchanged (i.e.
# the \ and the following character are both copied).

def expand(repl, regs, str):
    if '\\' not in repl:
        return repl
    new = ''
    i = 0
    ord0 = ord('0')
    while i < len(repl):
        c = repl[i]; i = i+1
        if c <> '\\' or i >= len(repl):
            new = new + c
        else:
            c = repl[i]; i = i+1
            if '0' <= c <= '9':
                a, b = regs[ord(c)-ord0]
                new = new + str[a:b]
            elif c == '\\':
                new = new + c
            else:
                new = new + '\\' + c
    return new


# Test program, reads sequences "pat repl str" from stdin.
# Optional argument specifies pattern used to split lines.

def test():
    import sys
    if sys.argv[1:]:
        delpat = sys.argv[1]
    else:
        delpat = '[ \t\n]+'
    while 1:
        if sys.stdin.isatty(): sys.stderr.write('--> ')
        line = sys.stdin.readline()
        if not line: break
        if line[-1] == '\n': line = line[:-1]
        fields = split(line, delpat)
        if len(fields) <> 3:
            print 'Sorry, not three fields'
            print 'split:', `fields`
            continue
        [pat, repl, str] = split(line, delpat)
        print 'sub :', `sub(pat, repl, str)`
        print 'gsub:', `gsub(pat, repl, str)`