I need to escape a & (ampersand) character in a string. The problem is whenever I string = string.replace ('&', '\&') the result is '\\&'. An extra backslash is added to escape the original backslash. How do I remove this extra backslash?
- Knowing zilch about python: string = string.replace('&', '&') ... maybe the replace method will escape that ampersand for you... hehiandisme– iandisme2010-02-01 19:43:27 +00:00Commented Feb 1, 2010 at 19:43
- 8If you still use SO, please mark a solution!erikbstack– erikbstack2012-08-07 08:51:16 +00:00Commented Aug 7, 2012 at 8:51
- 2@Veedrac: How is this 4 year old question marked as a duplicate of a question asked 6 days ago?User– User2014-06-12 15:46:25 +00:00Commented Jun 12, 2014 at 15:46
- 2@User Because the dupe has an accepted answer which is arguably more descriptive and explains the problem better than this oneBojangles– Bojangles2014-06-12 16:08:49 +00:00Commented Jun 12, 2014 at 16:08
- It was decided on Stack Overflow Chat that the new question should be made canonical. Thus everything else is officially a dupe of it. Any disagreements should go to Meta Stack Overflow for discussion.Veedrac– Veedrac2014-06-12 16:09:49 +00:00Commented Jun 12, 2014 at 16:09
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6 Answers
The result '\\&' is only displayed - actually the string is \&:
>>> str = '&' >>> new_str = str.replace('&', '\&') >>> new_str '\\&' >>> print new_str \& Try it in a shell.
2 Comments
erikbstack
Why is this not marked as solution?
DataOrc
The OP needs the literal string to be
'\&' not '\\&'.The extra backslash is not actually added; it's just added by the repr() function to indicate that it's a literal backslash. The Python interpreter uses the repr() function (which calls __repr__() on the object) when the result of an expression needs to be printed:
>>> '\\' '\\' >>> print '\\' \ >>> print '\\'.__repr__() '\\' 
Comments
Python treats \ in literal string in a special way.
This is so you can type '\n' to mean newline or '\t' to mean tab
Since '\&' doesn't mean anything special to Python, instead of causing an error, the Python lexical analyser implicitly adds the extra \ for you.
Really it is better to use \\& or r'\&' instead of '\&'
The r here means raw string and means that \ isn't treated specially unless it is right before the quote character at the start of the string.
In the interactive console, Python uses repr to display the result, so that is why you see the double '\'. If you print your string or use len(string) you will see that it is really only the 2 characters
Some examples
>>> 'Here\'s a backslash: \\' "Here's a backslash: \\" >>> print 'Here\'s a backslash: \\' Here's a backslash: \ >>> 'Here\'s a backslash: \\. Here\'s a double quote: ".' 'Here\'s a backslash: \\. Here\'s a double quote: ".' >>> print 'Here\'s a backslash: \\. Here\'s a double quote: ".' Here's a backslash: \. Here's a double quote ". To Clarify the point Peter makes in his comment see this link
Unlike Standard C, all unrecognized escape sequences are left in the string unchanged, i.e., the backslash is left in the string. (This behavior is useful when debugging: if an escape sequence is mistyped, the resulting output is more easily recognized as broken.) It is also important to note that the escape sequences marked as “(Unicode only)” in the table above fall into the category of unrecognized escapes for non-Unicode string literals.
2 Comments
Peter Hansen
Part of this isn't correct. Python does not "implicitly add the extra `` for you". It does, however, double the backslash when you display the repr() output of the string, as at prompt, purely for presentation purposes. len("\&") is only 2, proving there is no implicit munging of your data (thank heavens!).
Michael Mior
@PeterHansen I think the OP was pointing out that blackslashes should normally be escaped in non-raw strings so it would normally be written doubled.
>>> '\\&' == '\&' True >>> len('\\&') 2 >>> print('\\&') \& Or in other words: '\\&' only contains one backslash. It's just escaped in the python shell's output for clarity.
Comments
printing a list can also cause this problem (im new in python, so it confused me a bit too):
>>>myList = ['\\'] >>>print myList ['\\'] >>>print ''.join(myList) \ similarly:
>>>myList = ['\&'] >>>print myList ['\\&'] >>>print ''.join(myList) \& 
Comments
There is no extra backslash, it's just formatted that way in the interactive environment. Try:
print string Then you can see that there really is no extra backslash.
