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How would I add the "\" char to a string?

For instance, if I have "testme" and I do 

"testme"+"\"

I would get an error.

What is a "pythonic" approach for adding a "\" before each paren in a string?

For instance to go from "(hi)" to "\(hi\)"

My current approach is to iterate through each char and try to append a "\" which I feel isn't that "pythonic"

Andy
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2 Answers2

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Backslashes are used for escaping various characters, so to include a literal backslash in your string you need to use "\\", for example:

>>> print "testme" + "\\"
testme\

So to add a backslash before each paren in a string you could use the following:

s = s.replace('(', '\\(').replace(')', '\\)')

Or with regular expressions:

import re
s = re.sub(r'([()])', r'\\\1', s)

Note that you can also use a raw string literal by adding a the letter r before the opening quote, this makes it so that backslash is interpreted literally and no escaping is done. So r'foo\bar' would be the same as 'foo\\bar'. So you could rewrite the first approach like the following:

s = s.replace('(', r'\(').replace(')', r'\)')

Note that even in raw string literals you can use a backslash to escape the quotation mark used for the string literal, so r'we\'re' is the same as 'we\'re' or "we're". This is why raw string literals don't work well when you want the final character to be a backslash, for example r'testme\' (this will be a syntax error because the string literal is never closed).

Andrew Clark
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>>> import re  
>>> strs = "(hi)"
>>> re.sub(r'([()])',r'\\\g<0>',strs)
'\\(hi\\)'

"\" is invalid because you're escaping the closing quote here, so python will raise EOF error.

So you must escape the \ first using another \:

>>> "\\"
'\\'
>>> "\"
  File "<ipython-input-23-bdc6fd40f381>", line 1
    "\"
      ^
SyntaxError: EOL while scanning string literal

>>>
Ashwini Chaudhary
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