Python: decorator for converting parameters from possible yes/no values to bool

bool_param.py

import inspect
import functools
from distutils.util import strtobool


def tobool(yesno):
    """Convert all kinds of possible "yes" values to True/False."""
    return bool(strtobool(yesno))


def bool_param(*bool_args):
    """Convert given parameter possible yes/no values to True/False."""
    def convert_params_to_bool(func):
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            for bool_arg in bool_args:
                try:
                    # first see if we got it as a keyword argument
                    ba = kwargs.pop(bool_arg)
                    kwargs[bool_arg] = tobool(ba)
                except KeyError:
                    argspec = inspect.getargspec(func)
                    index = argspec.args.index(bool_arg)
                    # convert to mutable type, so we can modify it in place
                    args = list(args)
                    try:
                        # if did not get as a keyword arg, try to lookup if
                        # it has been given as positional argument
                        args[index] = tobool(args[index])
                    except IndexError:
                        # Not given as kwarg, neither arg, so we need default
                        # value corresponding to bool_arg variable
                        defaults = argspec.defaults or []
                        num_args = len(argspec.args) - len(defaults)
                        def_index = num_args - index
                        try:
                            kwargs[bool_arg] = tobool(defaults[def_index])
                        except IndexError:
                            # conform to python built in message when incorrect
                            # number of parameters have been given
                            message = ('{}() takes exactly {} arguments ({} given)'
                                       .format(func.__name__, num_args, len(args)))
                            raise TypeError(message)
            return func(*args, **kwargs)
        return wrapper
    return convert_params_to_bool

example_bool_param.py

@bool_param('param1')
def test1(param1, param2='noconvert'):
    print('PARAM1:', type(param1), param1)
    print('PARAM2:', type(param2), param2)
    
@bool_param('param1')
def test2(param1='yes', param2='noconvert'):
    print('PARAM1:', type(param1), param1)
    print('PARAM2:', type(param2), param2)

@bool_param('param1', 'param2')
def test3(param1='no', param2='yes'):
    print('PARAM1:', type(param1), param1)
    print('PARAM2:', type(param2), param2)
    

>>> test1('yes')
PARAM1: <type 'bool'> True
PARAM2: <type 'unicode'> noconvert

>>> test2()
PARAM1: <type 'bool'> True
PARAM2: <type 'unicode'> noconvert

>>> test3()
PARAM1: <type 'bool'> False
PARAM2: <type 'bool'> True