On Fri, Mar 25, 2011 at 12:30 AM, Paddy <paddy3...@googlemail.com> wrote: >>>> def fs(f, s): return [f(value) for value in s]
Note that your "fs" is basically equivalent to the "map" builtin, minus some of the features. >>>> fsf1 = partial(fs, f=f1) >>>> fsf1(s) > Traceback (most recent call last): > File "<pyshell#24>", line 1, in <module> > fsf1(s) > TypeError: fs() got multiple values for keyword argument 'f' >>>> # BUT >>>> fsf1(s=s) > [0, 2, 4, 6] >>>> > > Would someone help? When you invoke a partial application, it just adds the positional arguments passed to partial to the positional arguments passed in, and it adds the keyword arguments passed to partial to the keyword arguments passed in. Using partial to specify f as a keyword argument does not change the fact that it is also the first positional argument. So the call `partial(fs, f=f1)(s)` is equivalent to `fs(s, f=f1)`. In the latter case, 's' is being passed positionally as the first argument (i.e. 'f') and 'f1' is being passed by keyword as the 'f' argument, resulting in 'f' being passed in twice. The partial application is equivalent, so it does the same thing. The call `partial(fs, f=f1)(s=s)`, however, is equivalent to `fs(f=f1, s=s)`, which is fine. Moral of the story: if you pass in an argument by keyword, then the following arguments must be passed by keyword as well (or not at all), regardless of whether you're using partial or not. -- http://mail.python.org/mailman/listinfo/python-list
