How can I read a function's signature including default argument values?

Given a function object, how can I get its signature? For example, for:

def myMethod(firt, second, third='something'):
    pass

I would like to get "myMethod(firt, second, third='something')".

import inspect

def foo(a, b, x='blah'):
    pass

print(inspect.signature(foo))
# ArgSpec(args=['a', 'b', 'x'], varargs=None, keywords=None, defaults=('blah',))

Python 3.5+ recommends inspect.signature().

Arguably the easiest way to find the signature for a function would be help(function):

>>> def function(arg1, arg2="foo", *args, **kwargs): pass
>>> help(function)
Help on function function in module __main__:

function(arg1, arg2='foo', *args, **kwargs)

Also, in Python 3 a method was added to the inspect module called signature, which is designed to represent the signature of a callable object and its return annotation:

>>> from inspect import signature
>>> def foo(a, *, b:int, **kwargs):
...     pass

>>> sig = signature(foo)

>>> str(sig)
'(a, *, b:int, **kwargs)'

>>> str(sig.parameters['b'])
'b:int'

>>> sig.parameters['b'].annotation
<class 'int'>