Flexible Arguments: *args and **kwargs

Sometimes you do not know how many arguments will be passed. Python lets a parameter soak up any extra ones.

*args collects all extra positional arguments into a tuple:

def total(*args):
    result = 0
    for n in args:
        result += n
    return result

print(total(1, 2, 3))        # 6
print(total(10, 20))         # 30
print(total())               # 0

Inside the function, args is just a tuple you can loop over. The * is what does the collecting; the name args is only a convention.

**kwargs collects all extra keyword arguments into a dictionary:

def describe(**kwargs):
    parts = []
    for key, value in kwargs.items():
        parts.append(f"{key}={value}")
    return ", ".join(parts)

print(describe(name="Sam", age=30))   # name=Sam, age=30

You can combine fixed parameters with both. The order in the def is: normal parameters, then *args, then **kwargs:

def report(label, *args, **kwargs):
    return (label, args, kwargs)

print(report("scores", 9, 8, mode="avg"))
# ('scores', (9, 8), {'mode': 'avg'})