.format vs. %

[Stefan Krah]

Neil Cerutti <neilc at norwich.edu> wrote:
> On 2012-01-03, Stefan Krah <stefan-usenet at bytereef.org> wrote:
> > $ ./python -m timeit -n 1000000 '"%s" % 7.928137192'
> > 1000000 loops, best of 3: 0.0164 usec per loop
> 
> % is faster, but not by an order of magnitude.
> 
> On my machine:
> 
> C:\WINDOWS>python -m timeit -n 1000000 -s "n=7.92" "'%s' % n"
> 1000000 loops, best of 3: 0.965 usec per loop
> 
> C:\WINDOWS>python -m timeit -n 1000000 -s "n=7.92" "'{}'.format(n)"
> 1000000 loops, best of 3: 1.17 usec per loop

Indeed, I was a bit surprised by the magnitude of the difference.

Your timings seem to be in line with the difference seen in the
real-world benchmark. It isn't a big deal, considering that the
numeric formatting functions have to so many options, e.g:

>>> "{:020,}".format(712312312.2)
'00,000,712,312,312.2'


Still, it's nice to have a faster choice.


Stefan Krah