What does asterisk mean in Python?

Python

Asterisk

Programming

Python Syntax

Code Explanation

What does asterisk mean in Python?

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Python

Introduction

The asterisk (*) in Python serves seven different purposes depending on context: multiplication, exponentiation (**), unpacking iterables in function calls, collecting arguments in function definitions (*args, **kwargs), unpacking in assignments, merging collections, and forcing keyword-only arguments. Knowing which meaning applies comes down to recognizing where the * appears: in an expression, a function signature, or a data structure literal.

1. Multiplication and Exponentiation

python

1# Multiplication
2result = 5 * 3      # 15
3text = "ha" * 3     # "hahaha"
4zeros = [0] * 5     # [0, 0, 0, 0, 0]
5
6# Exponentiation
7result = 2 ** 10    # 1024
8result = 9 ** 0.5   # 3.0 (square root)

2. Unpacking Arguments in Function Calls

* unpacks an iterable into positional arguments. ** unpacks a dict into keyword arguments:

python

1def greet(first, last, greeting):
2    print(f"{greeting}, {first} {last}!")
3
4args = ["Alice", "Smith", "Hello"]
5greet(*args)  # Hello, Alice Smith!
6
7kwargs = {"first": "Bob", "last": "Jones", "greeting": "Hi"}
8greet(**kwargs)  # Hi, Bob Jones!
9
10# Combine both
11positional = ["Alice"]
12keyword = {"last": "Smith", "greeting": "Hey"}
13greet(*positional, **keyword)  # Hey, Alice Smith!

3. Collecting Arguments in Function Definitions

*args collects extra positional arguments into a tuple. **kwargs collects extra keyword arguments into a dict:

python

1def log(message, *args, **kwargs):
2    print(f"Message: {message}")
3    print(f"Extra args: {args}")        # tuple
4    print(f"Extra kwargs: {kwargs}")    # dict
5
6log("hello", 1, 2, 3, level="INFO", timestamp="now")
7# Message: hello
8# Extra args: (1, 2, 3)
9# Extra kwargs: {'level': 'INFO', 'timestamp': 'now'}

This is how functions like print() accept any number of arguments:

python

print("a", "b", "c", sep=", ")  # a, b, c
# print signature: print(*objects, sep=' ', end='\n', ...)

4. Keyword-Only Arguments

A bare * in a function signature forces all following parameters to be keyword-only:

python

1def connect(host, port, *, timeout=30, retries=3):
2    print(f"Connecting to {host}:{port}, timeout={timeout}")
3
4connect("localhost", 8080, timeout=60)     # OK
5connect("localhost", 8080, 60)             # TypeError: takes 2 positional arguments

Everything after * must be passed by name. This prevents ambiguous calls where argument order could be confused.

5. Unpacking in Assignments

python

1# Extended unpacking (Python 3)
2first, *rest = [1, 2, 3, 4, 5]
3print(first)  # 1
4print(rest)   # [2, 3, 4, 5]
5
6head, *middle, tail = [1, 2, 3, 4, 5]
7print(head)    # 1
8print(middle)  # [2, 3, 4]
9print(tail)    # 5
10
11*init, last = [1, 2, 3]
12print(init)  # [1, 2]
13print(last)  # 3

The *variable collects all remaining elements into a list.

6. Merging Collections

python

1# Merge lists (Python 3.5+)
2a = [1, 2, 3]
3b = [4, 5, 6]
4merged = [*a, *b]           # [1, 2, 3, 4, 5, 6]
5merged = [*a, 0, *b]        # [1, 2, 3, 0, 4, 5, 6]
6
7# Merge sets
8s1 = {1, 2}
9s2 = {3, 4}
10merged = {*s1, *s2}         # {1, 2, 3, 4}
11
12# Merge dicts (Python 3.5+)
13d1 = {"a": 1, "b": 2}
14d2 = {"b": 3, "c": 4}
15merged = {**d1, **d2}       # {"a": 1, "b": 3, "c": 4}
16# Later values overwrite earlier for duplicate keys
17
18# Dict merge operator (Python 3.9+)
19merged = d1 | d2            # {"a": 1, "b": 3, "c": 4}

7. In Type Hints

python

1from typing import Unpack, TypedDict
2
3# Variable positional args
4def process(*args: int) -> int:
5    return sum(args)
6
7# Variable keyword args (Python 3.12+)
8class Config(TypedDict):
9    timeout: int
10    retries: int
11
12def setup(**kwargs: Unpack[Config]) -> None:
13    pass

8. Positional-Only Parameters (Python 3.8+)

While / (not *) marks positional-only, they work together:

python

1def func(pos_only, /, normal, *, kw_only):
2    pass
3
4func(1, 2, kw_only=3)       # OK
5func(1, normal=2, kw_only=3) # OK
6func(pos_only=1, normal=2, kw_only=3)  # TypeError

Summary Table

Context	Syntax	Meaning
Expression	`a * b`	Multiplication
Expression	`a ** b`	Exponentiation
Function call	`f(*list)`	Unpack iterable into positional args
Function call	`f(**dict)`	Unpack dict into keyword args
Function def	`def f(*args)`	Collect extra positional args as tuple
Function def	`def f(**kwargs)`	Collect extra keyword args as dict
Function def	`def f(*, key)`	Force keyword-only arguments
Assignment	`a, *b = [1,2,3]`	Extended unpacking into list
Literal	`[a, b]`	Merge iterables
Literal	`{a, b}`	Merge dicts

Common Pitfalls

Mutable default with * repeat: [[]] * 3 creates [[], [], []] where all three lists are the SAME object. [[] for _ in range(3)] creates three independent lists.
*args is a tuple, not a list: You cannot use args.append(). Convert with list(args) if you need mutability.
**kwargs loses order in Python < 3.7: In Python 3.7+, dicts preserve insertion order. In earlier versions, kwargs order was undefined.
Unpacking in assignment requires iterable: a, *b = 5 raises TypeError because 5 is not iterable. The right side must be a sequence.
Double unpacking in function call: f(**d1, **d2) raises TypeError if d1 and d2 share keys (in Python < 3.9). Use f(**{**d1, **d2}) to merge first.

Summary

* has seven different meanings in Python depending on context
In expressions: multiplication (*) and power (**)
In function calls: unpack iterables (*list) and dicts (**dict) into arguments
In function definitions: collect extra args (*args) and kwargs (**kwargs)
Bare * in function signature forces keyword-only parameters
In assignments: extended unpacking (first, *rest = iterable)
In literals: merge collections ([*a, *b], {**d1, **d2})

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What does asterisk mean in Python?

Interview Questions practice on Codemia

Introduction

1. Multiplication and Exponentiation

2. Unpacking Arguments in Function Calls

3. Collecting Arguments in Function Definitions

4. Keyword-Only Arguments

5. Unpacking in Assignments

6. Merging Collections

7. In Type Hints

8. Positional-Only Parameters (Python 3.8+)

Summary Table

Common Pitfalls

Summary

Related reading

Tackling System Design Interview Problems

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Interview Questions practice on Codemia