Question

How would I do this with python :

if I have a string formatted like :

A..a.b.c

To make it like :

A.a.b.c

But I do not know beforehand how many dots I have ?

It’s like the tr -s function in linux

Answer 1

You want to replace every run of TWO or more dots by a single dot. That is achieved like this:

>>> import re
>>> re.sub(r'\.\.+', '.', 'A..a.b.c')
'A.a.b.c'

You don’t want and don’t need to replace every run of ONE or more dots by a single dot.

>>> re.sub(r'\.+', '.', 'A..a.b.c')
'A.a.b.c'

That produces the same result but does pointless substitutions of lone dots (3 on your example) and is consequently much slower.

Timings:

python -mtimeit -s"import re;subber=re.compile(r'\.+').sub;s=1000*'a.'" "subber('.',s)"
1000 loops, best of 3: 212 usec per loop

python -mtimeit -s"import re;subber=re.compile(r'\.\.+').sub;s=1000*'a.'" "subber('.',s)"
10000 loops, best of 3: 23.2 usec per loop