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).

Answer 1

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 (...)