How do I get the constructor signature for built-in types?

Discussion in 'Python' started by Steven D'Aprano, Jun 5, 2012.

  1. The inspect.getargspec and getfullargspec functions allow you to extract
    the function call signature for Python functions and methods. This allows
    you to work out the constructor signature for pure-Python classes, by
    calling inspect.getargspec on the __init__ or __new__ method.

    .... def __init__(self, a, b, *args):
    .... pass
    ....ArgSpec(args=['self', 'a', 'b'], varargs='args', keywords=None,

    So far so good. But if the __init__ method is inherited directly from a
    built-in, getargspec fails:

    .... pass
    ....Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "/usr/local/lib/python3.2/", line 794, in getargspec
    File "/usr/local/lib/python3.2/", line 821, in getfullargspec
    raise TypeError('{!r} is not a Python function'.format(func))
    TypeError: <slot wrapper '__init__' of 'object' objects> is not a Python

    How do I programmatically get the argument spec of built-in types'
    __init__ or __new__ methods?
    Steven D'Aprano, Jun 5, 2012
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