Which is faster?

[Terry Reedy]

"Aggelos I. Orfanakos" <aorfanakos at gmail.com> wrote in message 
news:1106793602.782397.61260 at z14g2000cwz.googlegroups.com...
> Any idea which of the following is faster?
>
> 'a/b/c/'[:-1]
> 'a/b/c/'.rstrip('/')

I find the first easier to read and mentally process.  Others may have a 
different answer.  But perhaps you meant with the CPython 2.x 
implementation ;-)

> P.S. I could time it but I thought of trying my luck here first, in
> case someone knows already, and of course the reason.

For more on the CPython (2.2) reason, consider

>>> def f1(s): return s[:-1]
...
>>> def f2(s): return s.rstrip('/')
...
>>> import dis
>>> dis.dis(f1)
          0 SET_LINENO               1

          3 SET_LINENO               1
          6 LOAD_FAST                0 (s)
          9 LOAD_CONST               1 (-1)
         12 SLICE+2
         13 RETURN_VALUE
         14 LOAD_CONST               0 (None)
         17 RETURN_VALUE
>>> dis.dis(f2)
          0 SET_LINENO               1

          3 SET_LINENO               1
          6 LOAD_FAST                0 (s)
          9 LOAD_ATTR                1 (rstrip)
         12 LOAD_CONST               1 ('/')
         15 CALL_FUNCTION            1
         18 RETURN_VALUE
         19 LOAD_CONST               0 (None)

The second has a load attribute (via dict lookup) that the first does not. 
More important, the second has a generic function call versus a specific 
byte-coded slice call.  The rstrip will also do a slice after it determines 
the endpoint of the slice.

Terry J. Reedy