How to substitute a numeric value in a string using Python?

Question

I need to modify a C source file using a Python script. How would I change this string:

#define MY_STRING      0

to:

#define MY_STRING      1

using a Python regular expression?

Ideally, the solution would accommodate an unknown number of spaces before the numeric value.

(Basically I don't know how to specify the original string minus the numeric value in the new string).

Sabuj Hassan · Accepted Answer · 2014-02-14 14:29:53Z

3

Use \s+ between the digit and the text for arbitrary number of spaces.

code = re.sub('define MY_STRING\s+0', 'define MY_STRING 1', code);

If you want to keep the same amount of spaces before the digit like original string, then you have to capture it and then use it on replacement.

code = re.sub('(define MY_STRING\s+)0', "\\1 1", code);
## \\1 is the captured group on regex inside (...)

edited Feb 14, 2014 at 14:29

answered Feb 14, 2014 at 13:55

Sabuj Hassan

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3 Comments

netdigger Over a year ago

Maybe throw in a #, a $ and a ^ there too..?

user1768576 Over a year ago

That's great and enough for my purpose, thanks. But I'm just curious to know how to provide the same number of spaces in the new string as were in the original?

Sabuj Hassan Over a year ago

@user1768576 Yes, you can do this as well. I have updated the answer.

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