Difficulty with maxsplit default value for str.split

[Nick Vatamaniuc]

Steven,

According to the current Python source the default value of
maxsplit=-1. I think you can count on that as I don't think there would
be a reason to change it in the future. If you are really worried about
it then your version of calling a particular version of split should
work.

By the way, if you use Python 2.5 and when your maxsplit function is
called there is a clear common case  in regards to maxsplit, you could
use the new conditional expression. Say most of the time mysplit is
used with a default value of maxsplit, then you can re-write your 'if'
code as
---------------------
result=S.split(sep) if maxsplit is None else S.split(sep,maxsplit)
---------------------

-Nick Vatamaniuc



Steven D'Aprano wrote:
> I'm having problems passing a default value to the maxsplit argument of
> str.split. I'm trying to write a function which acts as a wrapper to
> split, something like this:
>
> def mysplit(S, sep=None, maxsplit=None):
>     pre_processing()
>     result = S.split(sep, maxsplit)
>     post_processing()
>     return result
>
> But the split method doesn't accept a value of None for maxsplit, and I
> don't know what default value I should be using. Passing 0 as the default
> isn't correct, because then it splits zero times.
>
> By experimentation, I have discovered that passing -1 as the default
> instead of None *appears* to work, but I'm not sure if I can rely on it or
> if that is an accidental implementation detail. According to the
> documentation at
> http://docs.python.org/lib/string-methods.html#string-methods
>
> split([sep [,maxsplit]])
>     Return a list of the words in the string, using sep as the delimiter
>     string. If maxsplit is given, at most maxsplit splits are done. (thus,
>     the list will have at most maxsplit+1 elements). If maxsplit is not
>     specified, then there is no limit on the number of splits (all
>     possible splits are made).
>
>
> If I take that literally, then the correct way to wrap split is something
> like this:
>
> def mysplit(S, sep=None, maxsplit=None):
>     pre_processing()
>     if maxsplit is None:
>         # don't specify maxsplit
>         result = S.split(sep)
>     else:
>         result = S.split(sep, maxsplit)
>     post_processing()
>     return result
>
> Is it safe for me to pass -1 as the default to maxsplit, meaning
> "unlimited splits"? Should the docs be fixed to mention that?
> 
> Thanks,
> 
> 
> 
> -- 
> Steven.