args_kwargs

*args & **kwargs

Variable-length arguments and unpacking — essential for wrappers, decorators, and flexible APIs.

Files

File	Description
example.py	Collection, forwarding, and unpacking demos

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Descriptive Example

Scenario

Build a user profile from required and optional fields, then forward all arguments through a logging wrapper.

def build_profile(name, **kwargs):
    profile = {"name": name}
    profile.update(kwargs)
    return profile

result = build_profile("Alice", role="engineer", city="NYC", level="senior")
# {'name': 'Alice', 'role': 'engineer', 'city': 'NYC', 'level': 'senior'}

Forwarding in a decorator/wrapper

def log_call(func, *args, **kwargs):
    print(f"Calling {func.__name__} with {args=} {kwargs=}")
    return func(*args, **kwargs)

Unpacking at call site

def greet(greeting, name, punctuation="!"):
    return f"{greeting}, {name}{punctuation}"

args = ("Hello", "Bob")
kwargs = {"punctuation": "?"}
print(greet(*args, **kwargs))   # Hello, Bob?

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Interview Q&A

Q1: What do *args and **kwargs mean?
A: *args collects extra positional arguments into a tuple. **kwargs collects extra keyword arguments into a dict.

Q2: What is the correct parameter order in a function signature?
A: def f(pos_only, /, pos_or_kw, *args, kw_only, **kwargs). Positional-only, then regular, then *args, then keyword-only, then **kwargs.

Q3: What does * alone in a signature mean?
A: Everything after bare * is keyword-only. Example: def f(a, *, b) — b cannot be passed positionally.

Q4: How do you merge two dictionaries?
A: Python 3.9+: {**d1, **d2}. Earlier: {**d1, **d2} or d1 | d2 (3.9+). Later keys override earlier ones.

Q5: Why do decorators use *args, **kwargs?
A: So the wrapper accepts any signature and forwards all arguments to the original function unchanged.

Q6: What is argument unpacking vs collection?
A: Collection: def f(*args) gathers args into tuple. Unpacking: f(*my_list) spreads sequence into positional args.

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Run

python3 example.py