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Python Regular Expressions to implement string unescaping

Asked 2008-08-17T18:20:21.060
17

I am trying to implement string unescaping with Python regex and backreferences, and it doesn't seem to want to work very well. I'm sure it's something I'm doing wrong but I can't figure out what...

>>> import re
>>> mystring = r"This is \n a test \r"
>>> p = re.compile( "\\\\(\\S)" )
>>> p.sub( "\\1", mystring )
'This is n a test r'
>>> p.sub( "\\\\\\1", mystring )
'This is \\n a test \\r'
>>> p.sub( "\\\\1", mystring )
'This is \\1 a test \\1'

I'd like to replace \\[char] with \[char], but backreferences in Python don't appear to follow the same rules they do in every other implementation I've ever used. Could someone shed some light?

python regex backreference
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You are being tricked by Python's representation of the result string. The Python expression:

'This is \\n a test \\r'

represents the string

This is \n a test \r

which is I think what you wanted. Try adding 'print' in front of each of your p.sub() calls to print the actual string returned instead of a Python representation of the string.

>>> mystring = r"This is \n a test \r"
>>> mystring
'This is \\n a test \\r'
>>> print mystring
This is \n a test \r
answered 2008-08-17T19:26:33.250

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