[Python-ideas] Complicate str methods

[Serhiy Storchaka]

04.02.18 00:04, Franklin? Lee пише:
> Let s be a str. I propose to allow these existing str methods to take 
> params in new forms.
> 
> s.replace(old, new):
>      Allow passing in a collection of olds.
>      Allow passing in a single argument, a mapping of olds to news.
>      Allow the olds in the mapping to be tuples of strings.
> 
> s.split(sep), s.rsplit, s.partition:
>      Allow sep to be a collection of separators.
> 
> s.startswith, s.endswith:
>      Allow argument to be a collection of strings.
> 
> s.find, s.index, s.count, x in s:
>      Similar.
>      These methods are also in `list`, which can't distinguish between 
> items, subsequences, and subsets. However, `str` is already inconsistent 
> with `list` here: list.M looks for an item, while str.M looks for a 
> subsequence.
> 
> s.[r|l]strip:
>      Sadly, these functions already interpret their str arguments as 
> collections of characters.

The name of complicated str methods is regular expressions. For doing 
these operations efficiently you need to convert arguments in special 
optimized form. This is what re.compile() does. If make a compilation on 
every invocation of a str method, this will add too large overhead and 
kill performance.

Even for simple string search a regular expression can be more efficient 
than a str method.

$ ./python -m timeit -s 'import re; p = re.compile("spam"); s = 
"spa"*100+"m"' -- 'p.search(s)'
500000 loops, best of 5: 680 nsec per loop

$ ./python -m timeit -s 's = "spa"*100+"m"' -- 's.find("spam")'
200000 loops, best of 5: 1.09 usec per loop