Print function parameter names and values in Python

Question

When a function is called, I would like to print the names and values of it's parameters. Something like:

>>> def foo(bar, baz):
>>>    magic_parameter_printing() 
bar=0, baz=None

Right now I use format:

print("bar={},baz={}".format(bar,baz))

But this is a pain as new parameters get added, and there's always the risk of missing something.

I found this answer which can work for single variables when you know what they are (and uses eval), but I'd really like to be able to do it for all parameters a function is passed.

Answer 1

After you've add explanation how you want to apply this, I think best way will be to use decorator. It's more universal solution, because you can add it to any function in your code and it will print all debug info if debug mode is on.

Code:

from functools import wraps

DEBUG = True

def debug_log(function):
    @wraps(function)
    def wrapper(*args, **kwargs):
        if DEBUG:
            print(">> Called", function.__name__, "
",
                {**dict(zip(function.__code__.co_varnames, args)), **kwargs})
        result = function(*args, **kwargs)
        if DEBUG:
            print(">>", function.__name__, "return:
", result)
        return result
    return wrapper

@debug_log
def first_example(a, b, c):
    return 100

@debug_log
def second_example(d, e, f):
    return 200

first_example(10, 11, 12)
first_example(c=12, a=10, b=11)
second_example(13, 14, 15)
second_example(e=14, d=13, f=15)
DEBUG = False
first_example(0, 0, 0)
second_example(1, 1, 1)

Output:

>> Called first_example 
 {'a': 10, 'b': 11, 'c': 12}
>> first_example return:
 100
>> Called first_example 
 {'c': 12, 'a': 10, 'b': 11}
>> first_example return:
 100
>> Called second_example 
 {'d': 13, 'e': 14, 'f': 15}
>> second_example return:
 200
>> Called second_example 
 {'e': 14, 'd': 13, 'f': 15}
>> second_example return:
 200