python - Can't act with string's methods on a matched group -

i'm exercising standard regexp:

bill gates → gates, bill 

so do:

in [21]: re.sub("([^ ]+) (.+)", r"\2".upper() + r", \1", "bill gates") out[21]: 'gates, bill' 

why doesn't work? how 1 applies string methods matched string?

you uppercasing (part of) replacement pattern, not actual replacement result.

the r"\2".upper() + r", \1" expression results in value "\\2, \\1" before passing re.sub().

to dynamically process match groups, you'll need apply changes in function passed .sub() instead of replacement pattern:

def uppercase_last(match):     return "{}, {}".format(match.group(2).upper(), match.group(1))  re.sub("([^ ]+) (.+)", uppercase_last, "bill gates") 

demo:

>>> import re >>> def uppercase_last(match): ...     return "{}, {}".format(match.group(2).upper(), match.group(1)) ...  >>> re.sub("([^ ]+) (.+)", uppercase_last, "bill gates") 'gates, bill' 

alternatively, don't use regular expressions @ all:

>>> name = 'bill gates' >>> first, rest = name.split(none, 1) >>> "{}, {}".format(rest.upper(), first)