regular expression

On Fri, 25 Mar 2005 23:54:32 -0500, Peter Hansen <peter at engcorp.com> wrote:

>Bengt Richter wrote:>> On Sat, 26 Mar 2005 02:07:15 GMT, aaron <asteele at berkeley.edu> wrote:>>>>>>pattern.sub(':', '375 mi. south of U.C.B is 3.4 degrees warmer.')>>>'375 mi: south of U:C:B is 3.4 degrees warmer:'>>>>>>so this works, but not in the following case:>>>>>>pattern.sub(':', '.3')>>>>> Brute force the exceptional case that happens at the start of the line?>> >>  >>> import re>>  >>> pattern = re.compile(r'^[.]|(?!\d)[.](?!\d)')>>  >>> pattern.sub(':', '375 mi. south of U.C.B is 3.4 degrees warmer.')>>  '375 mi: south of U:C:B is 3.4 degrees warmer:'>>  >>> pattern.sub(':', '.3')>>  ':3'>>  >>> pattern.sub(':', '3.')>>  '3:'>>Be careful... the OP has assumed something that isn't true,>and Bengt's fix isn't sufficient:>> >>> import re> >>> s = 'x.3'> >>> pattern = re.compile(r'^[.]|(?!\d)[.](?!\d)')> >>> pattern.sub(':', '.3')>':3'> >>> pattern.sub(':', s)>'x.3'>>So the OP's "this works" comment was wrong.>>Suggestion: whip up a variety of automated test cases and>make sure you run them all whenever you make changes to>this code...>>(No, I don't have a solution to the continuing problem,>other than to wonder whether the input data really requires>all these edge cases to be handled properly.)>
Goes to show you ;-/ Do we need more tests than these?

 >>> import re>>> pattern = re.compile(r'[.](?!\d)|(?<!\d)[.]')>>> print pattern.sub(':', '375 mi. south of U.C.B is 3.4 degrees warmer.')
 375 mi: south of U:C:B is 3.4 degrees warmer:
 >>> for s,ss in ((s,pattern.sub(':', s)) for s in ('%s%s.%s%s'%(sp1,c1,c2,sp2)
 ...         for sp1 in ('', ' ')
 ...         for c1 in ('', 'x', '3')
 ...         for c2 in ('', 'x', '3')
 ...         for sp2 in ('', ' '))):
 ...     print '%10r => %r' %(s,ss)
 ...
        '.' => ':'
       '. ' => ': '
       '.x' => ':x'
      '.x ' => ':x '
       '.3' => ':3'
      '.3 ' => ':3 '
       'x.' => 'x:'
      'x. ' => 'x: '
      'x.x' => 'x:x'
     'x.x ' => 'x:x '
      'x.3' => 'x:3'
     'x.3 ' => 'x:3 '
       '3.' => '3:'
      '3. ' => '3: '
      '3.x' => '3:x'
     '3.x ' => '3:x '
      '3.3' => '3.3'
     '3.3 ' => '3.3 '
       ' .' => ' :'
      ' . ' => ' : '
      ' .x' => ' :x'
     ' .x ' => ' :x '
      ' .3' => ' :3'
     ' .3 ' => ' :3 '
      ' x.' => ' x:'
     ' x. ' => ' x: '
     ' x.x' => ' x:x'
    ' x.x ' => ' x:x '
     ' x.3' => ' x:3'
    ' x.3 ' => ' x:3 '
      ' 3.' => ' 3:'
     ' 3. ' => ' 3: '
     ' 3.x' => ' 3:x'
    ' 3.x ' => ' 3:x '
     ' 3.3' => ' 3.3'
    ' 3.3 ' => ' 3.3 '

Regards,
Bengt Richter