Using regex to add leading zeroes

Question

I would like to add a certain number of leading zeroes (say up to 3) to all numbers of a string. For example:

Input: /2009/5/song 01 of 12

Outpu

Answer 1

Another approach:

>>> x
'/2009/5/song 01 of 12'
>>> ''.join([i.isdigit() and i.zfill(4) or i for i in re.split("(?>>

Or:

>>> x
'/2009/5/song 01 of 12'
>>> r=re.split("(?>> ''.join(a+b.zfill(4) for a,b in zip(r[::2],r[1::2]))
'/2009/0005/song 0001 of 0012'