python - 计算有多少参数作为位置传递

Question

如果我有一个功能

def foo(x, y):
    pass

如何从函数内部判断 y是按位置传递还是使用关键字传递？
我想要类似的东西

def foo(x, y):
    if passed_positionally(y):
        print('y was passed positionally!')
    else:
        print('y was passed with its keyword')

所以我得到

>>> foo(3, 4)
y was passed positionally
>>> foo(3, y=4)
y was passed with its keyword

我意识到我最初没有指定这一点，但是可以在保留类型注释的同时做到这一点吗？到目前为止的最佳答案建议使用装饰器 - 但是，这不会保留返回类型

Answer 1

您可以创建一个装饰器，如下所示:

def checkargs(func):
    def inner(*args, **kwargs):
        if 'y' in kwargs:
            print('y passed with its keyword!')
        else:
            print('y passed positionally.')
        result = func(*args, **kwargs)
        return result
    return inner

>>>  @checkargs
...: def foo(x, y):
...:     return x + y

>>> foo(2, 3)
y passed positionally.
5

>>> foo(2, y=3)
y passed with its keyword!
5

当然，您可以通过允许装饰器接受参数来改进这一点。因此，您可以传递要检查的参数。这将是这样的:

def checkargs(param_to_check):
    def inner(func):
        def wrapper(*args, **kwargs):
            if param_to_check in kwargs:
                print('y passed with its keyword!')
            else:
                print('y passed positionally.')
            result = func(*args, **kwargs)
            return result
        return wrapper
    return inner

>>>  @checkargs(param_to_check='y')
...: def foo(x, y):
...:     return x + y

>>> foo(2, y=3)
y passed with its keyword!
5

我想添加 functools.wraps 将保留注释，以下版本还允许对所有参数执行检查(使用 inspect ):

from functools import wraps
import inspect

def checkargs(func):
    @wraps(func)
    def inner(*args, **kwargs):
        for param in inspect.signature(func).parameters:
            if param in kwargs:
                print(param, 'passed with its keyword!')
            else:
                print(param, 'passed positionally.')
        result = func(*args, **kwargs)
        return result
    return inner

>>>  @checkargs
...: def foo(x, y, z) -> int:
...:     return x + y

>>> foo(2, 3, z=4)
x passed positionally.
y passed positionally.
z passed with its keyword!
9

>>> inspect.getfullargspec(foo)
FullArgSpec(args=[], varargs='args', varkw='kwargs', defaults=None, 
kwonlyargs=[], kwonlydefaults=None, annotations={'return': <class 'int'>})
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