Class partial

Lib/functools.py:369–434

New function with partial application of the given arguments and keywords.

# Purely functional, no descriptor behaviour
class partial:
    """New function with partial application of the given arguments
    and keywords.
    """

    __slots__ = ("func", "args", "keywords", "_phcount", "_merger",
                 "__dict__", "__weakref__")

    __new__ = _partial_new
    __repr__ = recursive_repr()(_partial_repr)

    def __call__(self, /, *args, **keywords):
        phcount = self._phcount
        if phcount:
            try:
                pto_args = self._merger(self.args + args)
                args = args[phcount:]
            except IndexError:
                raise TypeError("missing positional arguments "
                                "in 'partial' call; expected "
                                f"at least {phcount}, got {len(args)}")
        else:
            pto_args = self.args
        keywords = {**self.keywords, **keywords}
        return self.func(*pto_args, *args, **keywords)

    def __get__(self, obj, objtype=None):
        if obj is None:
            return self
        return MethodType(self, obj)

    def __reduce__(self):
        return type(self), (self.func,), (self.func, self.args,
               self.keywords or None, self.__dict__ or None)

    def __setstate__(self, state):
        if not isinstance(state, tuple):
            raise TypeError("argument to __setstate__ must be a tuple")
        if len(state) != 4:
            raise TypeError(f"expected 4 items in state, got {len(state)}")
        func, args, kwds, namespace = state
        if (not callable(func) or not isinstance(args, tuple) or
           (kwds is not None and not isinstance(kwds, dict)) or
           (namespace is not None and not isinstance(namespace, dict))):
            raise TypeError("invalid partial state")

        if args and args[-1] is Placeholder:
            raise TypeError("trailing Placeholders are not allowed")
        phcount, merger = _partial_prepare_merger(args)

        args = tuple(args) # just in case it's a subclass
        if kwds is None:
            kwds = {}
        elif type(kwds) is not dict: # XXX does it need to be *exactly* dict?
            kwds = dict(kwds)
        if namespace is None:
            namespace = {}