Python *args和**kwargs的强制参数签名

>>> from inspect import Signature, Parameter
>>> # Make a signature for a func(x, y=42, *, z=None)
>>> parms = [ Parameter('x', Parameter.POSITIONAL_OR_KEYWORD),
...         Parameter('y', Parameter.POSITIONAL_OR_KEYWORD, default=42),
...         Parameter('z', Parameter.KEYWORD_ONLY, default=None) ]
>>> sig = Signature(parms)
>>> print(sig)
(x, y=42, *, z=None)
>>>

>>> def func(*args, **kwargs):
...     bound_values = sig.bind(*args, **kwargs)
...     for name, value in bound_values.arguments.items():
...         print(name,value)
...
>>> # Try various examples
>>> func(1, 2, z=3)
x 1
y 2
z 3
>>> func(1)
x 1
>>> func(1, z=3)
x 1
z 3
>>> func(y=2, x=1)
x 1
y 2
>>> func(1, 2, 3, 4)
Traceback (most recent call last):
...
    File "/usr/local/lib/python3.3/inspect.py", line 1972, in _bind
        raise TypeError('too many positional arguments')
TypeError: too many positional arguments
>>> func(y=2)
Traceback (most recent call last):
...
    File "/usr/local/lib/python3.3/inspect.py", line 1961, in _bind
        raise TypeError(msg) from None
TypeError: 'x' parameter lacking default value
>>> func(1, y=2, x=3)
Traceback (most recent call last):
...
    File "/usr/local/lib/python3.3/inspect.py", line 1985, in _bind
        '{arg!r}'.format(arg=param.name))
TypeError: multiple values for argument 'x'
>>>

from inspect import Signature, Parameter

def make_sig(*names):
    parms = [Parameter(name, Parameter.POSITIONAL_OR_KEYWORD)
            for name in names]
    return Signature(parms)

class Structure:
    __signature__ = make_sig()
    def __init__(self, *args, **kwargs):
        bound_values = self.__signature__.bind(*args, **kwargs)
        for name, value in bound_values.arguments.items():
            setattr(self, name, value)

# Example use
class Stock(Structure):
    __signature__ = make_sig('name', 'shares', 'price')

class Point(Structure):
    __signature__ = make_sig('x', 'y')

>>> import inspect
>>> print(inspect.signature(Stock))
(name, shares, price)
>>> s1 = Stock('ACME', 100, 490.1)
>>> s2 = Stock('ACME', 100)
Traceback (most recent call last):
...
TypeError: 'price' parameter lacking default value
>>> s3 = Stock('ACME', 100, 490.1, shares=50)
Traceback (most recent call last):
...
TypeError: multiple values for argument 'shares'
>>>

from inspect import Signature, Parameter

def make_sig(*names):
    parms = [Parameter(name, Parameter.POSITIONAL_OR_KEYWORD)
            for name in names]
    return Signature(parms)

class StructureMeta(type):
    def __new__(cls, clsname, bases, clsdict):
        clsdict['__signature__'] = make_sig(*clsdict.get('_fields',[]))
        return super().__new__(cls, clsname, bases, clsdict)

class Structure(metaclass=StructureMeta):
    _fields = []
    def __init__(self, *args, **kwargs):
        bound_values = self.__signature__.bind(*args, **kwargs)
        for name, value in bound_values.arguments.items():
            setattr(self, name, value)

# Example
class Stock(Structure):
    _fields = ['name', 'shares', 'price']

class Point(Structure):
    _fields = ['x', 'y']

>>> import inspect
>>> print(inspect.signature(Stock))
(name, shares, price)
>>> print(inspect.signature(Point))
(x, y)
>>>