Pierre Barbier de Reuille <pierre.barbier@cirad.fr> wrote:
Well, I want to come back on a point that wasn't discussed. I only found one positive comment here : http://mail.python.org/pipermail/python-dev/2005-August/055775.html
You apparently haven't been reading python-dev for around 36 hours, because there have been over a dozen positive comments in regards to str.partition().
Raymond Hettinger wrote:
* The function always succeeds unless the separator argument is not a string type or is an empty string. So, a typical call doesn't have to be wrapped in a try-suite for normal usage.
Well, I wonder if it's so good ! Almost all the use case I find would require something like:
head, sep, tail = s.partition(t) if sep: do something else: do something else
Why don't you pause for a second and read Raymond's post here: http://mail.python.org/pipermail/python-dev/2005-August/055781.html In that email there is a listing of standard library translations from str.find to str.partition, and in every case, it is improved. If you believe that str.index would be better used, take a moment and do a few translations of the sections provided and compare them with the str.partition examples.
Like, if you want to extract the drive letter from a windows path :
drive, sep, tail = path.partition(":") if not sep: drive = get_current_drive() # Because it's a local path
Or, if I want to iterate over all the path parts in a UNIX path:
sep = '/' while sep: head, sep, path = path.partition(sep)
IMO, that read strange ... partitionning until sep is None :S Then, testing with "if" in Python is always a lot slower than having an exception launched from C extension inside a try...except block.
In the vast majority of cases, all three portions of the returned partition result are used. The remaining few are generally split between one or two instances. In the microbenchmarks I've conducted, manually generating the slicings are measureably slower than when Python does it automatically. Also, exceptions are actually quite slow in relation to comparisons, specifically in the case of find vs. index (using 2.4)...
if 1: ... x = 'h' ... t = time.time() ... for i in xrange(1000000): ... if x.find('i')>=0: ... pass ... print time.time()-t ... 0.953000068665 if 1: ... x = 'h' ... t = time.time() ... for i in xrange(1000000): ... try: ... x.index('i') ... except ValueError: ... pass ... print time.time()-t ... 6.53100013733
I urge you to take some time to read Raymond's translations. - Josiah