How to string.replace once starting from the right?
I could do it from the left.
>>> x = 'foo bar bar'
>>> x.replace(' ', ' X ', 1)
'foo X bar bar'
Or with re.sub:
>>> import re
>>> re.sub(' ', ' X ', x, 1)
'foo X bar bar'
From the right, i could do:
>>> x = 'foo bar bar'
>>> x[::-1].replace(' ', ' X ', 1)[::-1]
'foo bar X bar'
But is there any other way to replace once starting from the right?
First of all, I think you're approach is ok. Oneliner, pretty pythonic.
The question suggested in the comments (Right-to-left string replace in Python?) provide several useful answers that worth measuring them.
One is the same approach you're taking: x[::-1].replace(' ', ' X ', 1)[::-1] and the other one is with rsplit and join.
I profiled both and this was the output I got:
$python -mtimeit -s "s = 'foo bar bar'" "s[::-1].replace(' ', ' X ', 1)[::-1]"
1000000 loops, best of 3: 1.18 usec per loop
$python -mtimeit -s "s = 'foo bar bar'" "' X '.join(s.rsplit(' ',1))"
1000000 loops, best of 3: 0.8 usec per loop
So my recommendation is the second approach which seems a lot faster. That being said, whichever you chose, put a comment beside telling # this is right replacing! because either way is pretty unclear what the code does :)
Hope this helps!
