python re.sub - alternative replacement patterns

Question

I want to provide alternative replacement patterns to re.sub.

Let's say i've got two search patterns as alternatives, like this:

re.sub(r"[A-Z]+|[a-z]+", replacementpattern, string)

and instead of providing one replacement pattern I would like to somehow catch which search pattern alternative was matched and provide alternative replacement patterns. Is this possible? Thanks.

PS. code specifics here are irrelevant, it's a general question.

Answer 1

You can pass a function to re.sub(). In the function you can return the value needed based on the captured group. A simple code for illustration:

>>> def fun(m):
...   if m:
...     if m.group(1):
...        return 'x'
...     else:
...        return 'y'


>>>print re.sub(r"([A-Z]+)|([a-z]+)", fun , "ab")

The function fun() checks if the match succeeded and based on the captured group, returns the replacement string. If [A-Z]+ was matched, x is the replacement string else [a-z]+ was matched and y is the replacement string.

For more information : doc

Answer 2

Usually, you would just use two replacements:

re.sub(r"[A-Z]+", replacement1, string)
re.sub(r"[a-z]+", replacement2, string)

Anticlimactic, right?

It's actually less code than the alternatives usually, and it's far clearer what you're doing.