How to escape “\” characters in python

Question

i am very new to regular expression and trying get \"\\\" character using python

normally i can escape \"\\\" like this

print (\"\\\\\");
print (\"         


        

Answer 1

EDIT: The problem is actually how print works with lists & strings. It prints the representation of the string, not the string itself, the representation of a string containing just a backslash is '\\'. So findall is actually finding the single backslash correctly, but print isn't printing it as you'd expect. Try:

>>> print(re.findall(r'\\',"i am \\nit")[0])
\

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(The following is my original answer, it can be ignored (it's entirely irrelevant), I'd misinterpreted the question initially. But it seems to have been upvoted a bit, so I'll leave it here.)

The r prefix on a string means the string is in "raw" mode, that is, \ are not treated as special characters (it doesn't have anything to do with "regex").

However, r'\' doesn't work, as you can't end a raw string with a backslash, it's stated in the docs:

Even in a raw string, string quotes can be escaped with a backslash, but the backslash remains in the string; for example, r"\"" is a valid string literal consisting of two characters: a backslash and a double quote; r"\" is not a valid string literal (even a raw string cannot end in an odd number of backslashes). Specifically, a raw string cannot end in a single backslash (since the backslash would escape the following quote character).

But you actually can use a non-raw string to get a single backslash: "\\".

Answer 2

It is unnecessary to escape backslashes in raw strings, unless the backslash immediately precedes the closing quote.

Answer 3

Note that you're using two different kinds of string literal here -- there's the regular string "a string" and the raw string r"a raw string". Regular string literals observe backslash escaping, so to actually put a backslash in the string, you need to escape it too. Raw string literals treat backslashes like any other character, so you're more limited in which characters you can actually put in the string (no specials that need an escape code) but it's easier to enter things like regular expressions, because you don't need to double up backslashes if you need to add a backslash to have meaning inside the string, not just when creating the string.

Answer 4

can someone please explain why

Because re.findall found one match, and the match text consisted of a backslash. It gave you a list with one element, which is a string, which has one character, which is a backslash.

That is written ['\\'] because '\\' is how you write "a string with one backslash" - just like you had to do when you wrote the example code print "\\".