The official doc of the partial function from the functools stdlib module says
it "is used for partial function application which “freezes” some portion of a
function’s arguments and/or keywords resulting in a new object with a
simplified signature".
However, whereas positional arguments are effectively "frozen" (cannot be
altered in the partial object), keyword arguments can in fact not be frozen as
they always will be overridden by the ones passed to the partial object.
The "and/or keywords" part in the quote above thus sounds wrong when applied to
the current implementation, and is more accurately describing the following
situation :
def partial(func, /, *args, **keywords):
def newfunc(*fargs, **fkeywords):
return func(*args, *fargs, **keywords, **fkeywords) # instead of the
current func(*args, *fargs, **{**keywords, **fkeywords}) value
newfunc.func = func
newfunc.args = args
newfunc.keywords = keywords
return newfunc
Shouldn't we provide the above implementation - which really freezes the given
positional AND keyword arguments - in a new partial function to be added to the
functools module, and fix the docs accordingly ?
On the signature side, we would also actually always get a "new object with a
simplified signature" as stated in the doc, which is not the case currently.
If we consider the following code :
import functools
def F(arg, opt = 'BaseValue') :
return (arg, opt)
G = functools.partial(F, opt = 'NewValue')
the partial function G's signature is (arg, opt = 'NewValue') and is not really
simplified compared to the initial (arg, opt = 'BaseValue') one.
The only effect of partial on the function signature is to alter the default
values of the specified keyword arguments.
With the proposed implementation, the signature would actually be simplified to
(arg).
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