Default Argument decorator python

Question

Python 3.6

I am trying to create a decorator that automatically assigns an argument string as the default value.

eg:

def example(one='one', two='two', three='three'):
    pass

will be equivalent to:

@DefaultArguments
def example(one, two, three):
    pass

Here is my attempt (not working .. else ..) DefaultArguments:

from inspect import Parameter, Signature, signature


class DefaultArguments(object):

    @staticmethod
    def default_signature(signature):
        def default(param):
            if param.kind in (Parameter.POSITIONAL_OR_KEYWORD, Parameter.POSITIONAL_ONLY):
                return param.replace(default=param.name)
            else:
                return param
        return Signature([default(param) for param in signature.parameters.values()])

    def __init__(self, func):
        self.func = func
        self.sig = self.default_signature(signature(func))

    def __call__(self, *args, **kwargs):
        arguments = self.sig.bind(*args, **kwargs)
        return self.func(arguments)

The static method default_signaturecreates the desired signature for the function, but it's hard for me to assign a new signature to the function. I am trying to use Signature. bindI read the docs , but I missed something.

EDIT

Including Ashvini Chodhari in response:

from inspect import Parameter, Signature, signature

class DefaultArguments(object):

    @staticmethod
    def default_signature(signature):
        def default(param):
            if param.kind in (Parameter.POSITIONAL_OR_KEYWORD, Parameter.POSITIONAL_ONLY):
                return param.replace(default=param.name)
            else:
                return param
        return Signature([default(param) for param in signature.parameters.values()])

    def __init__(self, func):
        self.func = func
        self.sig = self.default_signature(signature(func))
        print(self.sig)

    def __call__(self, *args, **kwargs):
        ba = self.sig.bind(*args, **kwargs)
        ba.apply_defaults()
        return self.func(*ba.args, **ba.kwargs)

Answer 1

apply_defaults BoundArguments .

BoundArguments args kwargs.

def __call__(self, *args, **kwargs):
    ba = self.sig.bind(*args, **kwargs)
    ba.apply_defaults()
    return self.func(*ba.args, **ba.kwargs)

Demo:

>>> @DefaultArguments
... def example(one, two, three):
...         print(one, two, three)
...

>>> example()
one two three
>>> example('spam')
spam two three
>>> example(one='spam', three='eggs')
spam two eggs

---

, :

from functools import wraps
from inspect import Parameter, Signature, signature


def default_arguments(func):

    def default(param):
        if param.kind in (Parameter.POSITIONAL_OR_KEYWORD, Parameter.POSITIONAL_ONLY):
            param = param.replace(default=param.name)
        return param

    sig = Signature([default(param) for param in signature(func).parameters.values()])

    @wraps(func)
    def wrapper(*args, **kwargs):
        ba = sig.bind(*args, **kwargs)
        ba.apply_defaults()
        return func(*ba.args, **ba.kwargs)

    wrapper.__signature__ = sig
    return wrapper

Demo:

>>> from inspect import getfullargspec    
>>> @default_arguments
... def example(one, two, three):
...         print(one, two, three)
...

>>> getfullargspec(example)
FullArgSpec(
    args=['one', 'two', 'three'],
    varargs=None,
    varkw=None,
    defaults=('one', 'two', 'three'),
    kwonlyargs=[], kwonlydefaults=None, annotations={}
)

Answer 2

:

import inspect

def default_args(func):
    argspec = inspect.getfullargspec(func)

    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        unpassed_positional_args = argspec.args[len(args):]
        kwargs.update((a, a) for a in unpassed_positional_args if a not in kwargs)
        return func(*args, **kwargs)

    return wrapper

, python. :

def foo(a, b):
    ...

:

foo(b=1, a=2)

, , , , . kwargs dict.

, - python2.x, getfullargspec getargspec, .

---

:

Ashwini , 10 , :

@default_args
def foo(a, b, c):
    pass

@DefaultArguments
def bar(a, b, c):
    pass

@default_arguments
def qux(a, b, c):
    pass

import timeit
print(timeit.timeit('foo()', 'from __main__ import foo'))  # 1.72s
print(timeit.timeit('bar()', 'from __main__ import bar'))  # 17.4s
print(timeit.timeit('qux()', 'from __main__ import qux'))  # 17.6

__signature__ ( ). , Signature __signature__, argspec ...