CODEWITHSUNDEEP
pythonregexwindowsfunction
user1586464
user1586464

Reputation: 257

Call functions from re.sub

This is a simple example:

import re

math='<m>3+5</m>'
print re.sub(r'<(.)>(\d+?)\+(\d+?)</\1>', int(r'\2') + int(r'\3'), math)

It gives me this error:

ValueError: invalid literal for int() with base 10: '\\2'

It sends \\2 instead of 3 and 5.

Why? How do I solve it?

Upvotes: 16

Views: 9641

Answers (2)

xdazz
xdazz

Reputation: 160893

You need to use lambda function.

print re.sub(r'<(.)>(\d+?)\+(\d+?)</\1>', lambda m: str(int(m.group(2)) + int(m.group(3))), math)

Upvotes: 7

BrenBarn
BrenBarn

Reputation: 251468

If you want to use a function with re.sub you need to pass a function, not an expression. As documented here, your function should take the match object as an argument and returns the replacement string. You can access the groups with the usual .group(n) methods and so on. An example:

re.sub("(a+)(b+)", lambda match: "{0} as and {1} bs ".format(
    len(match.group(1)), len(match.group(2))
), "aaabbaabbbaaaabb")
# Output is '3 as and 2 bs 2 as and 3 bs 4 as and 2 bs '

Note that the function should return strings (since they will be put back into the original string).

Upvotes: 28

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