Python *args and **kwargs explained

Variable Arguments

*args collects extra positional arguments into a tuple. **kwargs collects extra keyword arguments into a dictionary. Both names are conventional — only the * and ** matter.

def add(*numbers):
    return sum(numbers)

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

def describe(**info):
    for k, v in info.items():
        print(f"{k}: {v}")

describe(name="Alice", age=30, city="NY")

Combining All Types

Argument order rule: positional → *args → keyword-only → **kwargs. Breaking this order raises a SyntaxError.

def mixed(a, b, *args, sep=" ", **kwargs):
    print(a, b, args, sep, kwargs)

mixed(1, 2, 3, 4, sep=",", x=10)
# 1 2 (3, 4) , {'x': 10}

Unpacking on the Call Side

nums = [1, 2, 3]
print(add(*nums))   # unpack list as positional args

params = {"name": "Alice", "age": 30}
describe(**params)  # unpack dict as keyword args

The *args and **kwargs pattern is used extensively in Python libraries for building flexible APIs, wrappers, and decorators that need to forward arguments transparently. When writing a decorator, always accept *args, **kwargs in the wrapper so it can wrap any function regardless of signature. Positional-only parameters (before a / in the signature) and keyword-only parameters (after a bare *) are advanced signature constraints introduced in Python 3 that library authors use to control how their APIs are called.