Using a regular expression to replace upper case repeated letters in python with a single lowercase letter

python regex capitalization

Pass a function as the repl argument. The MatchObject is passed to this function and .group(1) gives the first parenthesized subgroup:

import res = 'start TT end'callback = lambda pat: pat.group(1).lower()re.sub(r'([A-Z]){2}', callback, s)

EDIT
And yes, you should use ([A-Z])\1 instead of ([A-Z]){2} in order to not match e.g. AZ. (See @bobince's answer.)

import res = 'start TT end're.sub(r'([A-Z])\1', lambda pat: pat.group(1).lower(), s) # Inline

Gives:

'start t end'

python regex capitalization

You can't change case in a replacement string. You would need a replacement function:

>>> def replacement(match):...     return match.group(1).lower()... >>> re.sub(r'([A-Z])\1', replacement, 'start TT end')'start t end'

python regex capitalization

You can do it with a regular expression, just pass a function as the replacement like the docs say. The problem is your pattern.

As it is, your pattern matches runs of any two capital letters. I'll leave the actual pattern to you, but it starts with AA|BB|CC|.

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