Lib/reconvert.py

   1 #! /usr/bin/env python1.5
   2
   3 """Convert old ("regex") regular expressions to new syntax ("re").
   4
   5 When imported as a module, there are two functions, with their own
   6 strings:
   7
   8   convert(s, syntax=None) -- convert a regex regular expression to re syntax
   9
  10   quote(s) -- return a quoted string literal
  11
  12 When used as a script, read a Python string literal (or any other
  13 expression evaluating to a string) from stdin, and write the
  14 translated expression to stdout as a string literal.  Unless stdout is
  15 a tty, no trailing \n is written to stdout.  This is done so that it
  16 can be used with Emacs C-U M-| (shell-command-on-region with argument
  17 which filters the region through the shell command).
  18
  19 No attempt has been made at coding for performance.
  20
  21 Translation table...
  22
  23     \(    (     (unless RE_NO_BK_PARENS set)
  24     \)    )     (unless RE_NO_BK_PARENS set)
  25     \|    |     (unless RE_NO_BK_VBAR set)
  26     \<    \b    (not quite the same, but alla...)
  27     \>    \b    (not quite the same, but alla...)
  28     \`    \A
  29     \'    \Z
  30
  31 Not translated...
  32
  33     .
  34     ^
  35     $
  36     *
  37     +           (unless RE_BK_PLUS_QM set, then to \+)
  38     ?           (unless RE_BK_PLUS_QM set, then to \?)
  39     \
  40     \b
  41     \B
  42     \w
  43     \W
  44     \1 ... \9
  45
  46 Special cases...
  47
  48     Non-printable characters are always replaced by their 3-digit
  49     escape code (except \t, \n, \r, which use mnemonic escapes)
  50
  51     Newline is turned into | when RE_NEWLINE_OR is set
  52
  53 XXX To be done...
  54
  55     [...]     (different treatment of backslashed items?)
  56     [^...]    (different treatment of backslashed items?)
  57     ^ $ * + ? (in some error contexts these are probably treated differently)
  58     \vDD  \DD (in the regex docs but only works when RE_ANSI_HEX set)
  59
  60 """
  61
  62
  63 import regex
  64 from regex_syntax import * # RE_*
  65
  66 # Default translation table
  67 mastertable = {
  68     r'\<': r'\b',
  69     r'\>': r'\b',
  70     r'\`': r'\A',
  71     r'\'': r'\Z',
  72     r'\(': '(',
  73     r'\)': ')',
  74     r'\|': '|',
  75     '(': r'\(',
  76     ')': r'\)',
  77     '|': r'\|',
  78     '\t': r'\t',
  79     '\n': r'\n',
  80     '\r': r'\r',
  81 }
  82
  83
  84 def convert(s, syntax=None):
  85     """Convert a regex regular expression to re syntax.
  86
  87     The first argument is the regular expression, as a string object,
  88     just like it would be passed to regex.compile().  (I.e., pass the
  89     actual string object -- string quotes must already have been
  90     removed and the standard escape processing has already been done,
  91     e.g. by eval().)
  92
  93     The optional second argument is the regex syntax variant to be
  94     used.  This is an integer mask as passed to regex.set_syntax();
  95     the flag bits are defined in regex_syntax.  When not specified, or
  96     when None is given, the current regex syntax mask (as retrieved by
  97     regex.get_syntax()) is used -- which is 0 by default.
  98
  99     The return value is a regular expression, as a string object that
 100     could be passed to re.compile().  (I.e., no string quotes have
 101     been added -- use quote() below, or repr().)
 102
 103     The conversion is not always guaranteed to be correct.  More
 104     syntactical analysis should be performed to detect borderline
 105     cases and decide what to do with them.  For example, 'x*?' is not
 106     translated correctly.
 107
 108     """
 109     table = mastertable.copy()
 110     if syntax is None:
 111         syntax = regex.get_syntax()
 112     if syntax & RE_NO_BK_PARENS:
 113         del table[r'\('], table[r'\)']
 114         del table['('], table[')']
 115     if syntax & RE_NO_BK_VBAR:
 116         del table[r'\|']
 117         del table['|']
 118     if syntax & RE_BK_PLUS_QM:
 119         table['+'] = r'\+'
 120         table['?'] = r'\?'
 121         table[r'\+'] = '+'
 122         table[r'\?'] = '?'
 123     if syntax & RE_NEWLINE_OR:
 124         table['\n'] = '|'
 125     res = ""
 126
 127     i = 0
 128     end = len(s)
 129     while i < end:
 130         c = s[i]
 131         i = i+1
 132         if c == '\\':
 133             c = s[i]
 134             i = i+1
 135             key = '\\' + c
 136             key = table.get(key, key)
 137             res = res + key
 138         else:
 139             c = table.get(c, c)
 140             res = res + c
 141     return res
 142
 143
 144 def quote(s, quote=None):
 145     """Convert a string object to a quoted string literal.
 146
 147     This is similar to repr() but will return a "raw" string (r'...'
 148     or r"...") when the string contains backslashes, instead of
 149     doubling all backslashes.  The resulting string does *not* always
 150     evaluate to the same string as the original; however it will do
 151     just the right thing when passed into re.compile().
 152
 153     The optional second argument forces the string quote; it must be
 154     a single character which is a valid Python string quote.
 155
 156     """
 157     if quote is None:
 158         q = "'"
 159         altq = "'"
 160         if q in s and altq not in s:
 161             q = altq
 162     else:
 163         assert quote in ('"', "'")
 164         q = quote
 165     res = q
 166     for c in s:
 167         if c == q: c = '\\' + c
 168         elif c < ' ' or c > '~': c = "\\%03o" % ord(c)
 169         res = res + c
 170     res = res + q
 171     if '\\' in res:
 172         res = 'r' + res
 173     return res
 174
 175
 176 def main():
 177     """Main program -- called when run as a script."""
 178     import sys
 179     s = eval(sys.stdin.read())
 180     sys.stdout.write(quote(convert(s)))
 181     if sys.stdout.isatty():
 182         sys.stdout.write("\n")
 183
 184
 185 if __name__ == '__main__':
 186     main()