import inspect
def get_arg_value(func, argname, args, kwargs):
"""
This function is meant to be used inside decorators, when you want
to find what value will be available inside a wrapped function for
a particular argument name. It handles positional and keyword
arguments and takes into account default values. For example:
>>> def foo(x, y): pass
...
>>> get_arg_value(foo, 'y', [1, 2], {})
2
>>> get_arg_value(foo, 'y', [1], {'y' : 2})
2
>>> def foo(x, y, z=300): pass
...
>>> get_arg_value(foo, 'z', [1], {'y' : 2})
300
>>> get_arg_value(foo, 'z', [1], {'y' : 2, 'z' : 5})
5
"""
# first check kwargs
if argname in kwargs:
return kwargs[argname]
# OK. could it be a positional argument?
regargs, varargs, varkwargs, defaults=inspect.getargspec(func)
if argname in regargs:
regdict=dict(zip(regargs, args))
if argname in regdict:
return regdict[argname]
defaultdict=dict(zip(reversed(regargs), defaults))
if argname in defaultdict:
return defaultdict[argname]
raise ValueError("no such argument: %s" % argname)
