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

Sorry its a bit messy. I modified some code from Easy Dump of Function Arguments in the PythonDecoratorLibrary.

def dump_args(func):
    "This decorator dumps out the arguments passed to a function before calling it"
    argnames = func.func_code.co_varnames[:func.func_code.co_argcount]
    fname = func.func_name
    def echo_func(*args,**kwargs):
        print fname, "(", ', '.join(
            '%s=%r' % entry
            for entry in zip(argnames,args[:len(argnames)])+[("args",list(args[len(argnames):]))]+[("kwargs",kwargs)]) +")"
    return echo_func

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

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

Output:

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