python - Decorator that prints function call details (parameters names and effective values)?

Question

I want to make a function that being a decorator to another function will print that function call details - parameters names and effective values. My current implementation is this.

def describeFuncCall(func):
    """
    Decorator to print function call details.

    parameters names and effective values.
    """

    def wrapper(*func_args, **func_kwargs):
        print "func_code.co_varnames =", func.func_code.co_varnames
        print "func_code.co_argcount =", func.func_code.co_argcount
        print "func_args =", func_args
        print "func_kwargs =", func_kwargs
        params = []
        for argNo in range(func.func_code.co_argcount):
            argName = func.func_code.co_varnames[argNo]
            argValue = (
                func_args[argNo]
                if argNo < len(func_args)
                else func.func_defaults[argNo - func.func_code.co_argcount]
            )
            params.append((argName, argValue))
        for argName, argValue in func_kwargs.items():
            params.append((argName, argValue))
        params = [argName + " = " + repr(argValue)
                  for argName, argValue in params]
        print (func.__name__ + " ( " + ", ".join(params) + " )")
        return func(*func_args, **func_kwargs)

    return wrapper


@describeFuncCall
def test(a, b=4, c="blah-blah", *args, **kwargs):
    pass


test(1)
# test(1, 3)
# test(1, d = 5)
test(1, 2, 3, 4, 5, d=6, g=12.9)

Kinda works, but with some bugs:

For call

test(1, 2, 3, 4, 5, d = 6, g = 12.9)

it prints

test ( a = 1, b = 2, c = 3, d = 6, g = 12.9 ).

The expected result is

test ( a = 1, b = 2, c = 3, args = [4, 5], kwargs = {'d': 6, 'g': 12.9} )

I got stuck here. Can you help me to find the right solution?

Answer 1

Here is the updated version for Python 3.6+

import inspect


def dump_args(func):
    """
    Decorator to print function call details.

    This includes parameters names and effective values.
    """

    def wrapper(*args, **kwargs):
        func_args = inspect.signature(func).bind(*args, **kwargs).arguments
        func_args_str = ", ".join(map("{0[0]} = {0[1]!r}".format, func_args.items()))
        print(f"{func.__module__}.{func.__qualname__} ( {func_args_str} )")
        return func(*args, **kwargs)

    return wrapper


@dump_args
def test(a, b=4, c="blah-blah", *args, **kwargs):
    pass


test(1)
test(1, 3)
test(1, d=5)
test(1, 2, 3, 4, 5, d=6, g=12.9)

---

Old version

---

Working version with default values:

def dumpArgs(func):
    '''Decorator to print function call details - parameters names and effective values'''
    def wrapper(*func_args, **func_kwargs):
        arg_names = func.func_code.co_varnames[:func.func_code.co_argcount]
        args = func_args[:len(arg_names)]
        defaults = func.func_defaults or ()
        args = args + defaults[len(defaults) - (func.func_code.co_argcount - len(args)):]
        params = zip(arg_names, args)
        args = func_args[len(arg_names):]
        if args: params.append(('args', args))
        if func_kwargs: params.append(('kwargs', func_kwargs))
        print func.func_name + ' (' + ', '.join('%s = %r' % p for p in params) + ' )'
        return func(*func_args, **func_kwargs)
    return wrapper  

@dumpArgs
def test(a, b = 4, c = 'blah-blah', *args, **kwargs):
    pass

test(1)
test(1, 3)
test(1, d = 5)
test(1, 2, 3, 4, 5, d = 6, g = 12.9)

Result:

>>> test  (  a = 1, b = 4, c = 'blah-blah' )
test  (  a = 1, b = 3, c = 'blah-blah' )
test  (  a = 1, b = 4, c = 'blah-blah', kwargs = {'d': 5} )
test  (  a = 1, b = 2, c = 3, args = (4, 5), kwargs = {'d': 6, 'g': 12.9} )