How to Use Default Parameter Values in Python Functions

Shows how to define and call Python functions with default parameter values, including overriding some or all defaults and using keyword arguments.

Easy Python 3.9+ Aug 9, 2026 Functions & basics 14 views 0 copies

functions default-parameters arguments basics

Python code

23 lines

Python 3.9+

def greet(name, greeting="Hello", punctuation="!"):
    """Return a greeting message using default parameters."""
    return f"{greeting}, {name}{punctuation}"

if __name__ == "__main__":
    # Using defaults
    print(greet("Alice"))
    
    # Overriding first default
    print(greet("Bob", "Hi"))
    
    # Overriding both defaults
    print(greet("Charlie", "Hey", "."))
    
    # Using keyword arguments
    print(greet("Diana", punctuation="?"))
    
    # Validating default behavior
    assert greet("Alice") == "Hello, Alice!"
    assert greet("Bob", "Hi") == "Hi, Bob!"
    assert greet("Charlie", "Hey", ".") == "Hey, Charlie."
    assert greet("Diana", punctuation="?") == "Hello, Diana?"
    print("All assertions passed.")

Output

stdout

Hello, Alice!
Hi, Bob!
Hey, Charlie.
Hello, Diana?
All assertions passed.

How it works

Default parameters let you call a function with fewer arguments than its full signature, filling in missing values automatically. The defaults are evaluated when the function is defined, not each time it's called. You can override individual defaults by passing values positionally or by name with keyword arguments. Keyword arguments make it clear which parameter you're setting and let you skip earlier defaults. This pattern keeps functions flexible while avoiding repetitive code.

Common mistakes

Using mutable defaults like lists or dicts, which persist between calls
Putting parameters with defaults before required parameters in the signature
Forgetting that keyword arguments must come after positional ones in a call

Variations

Use *args and **kwargs to accept variable numbers of arguments with defaults
Use functools.partial to fix default values at call time instead of definition time

Real-world use cases

Building reusable log formatters where the log level and timestamp format have sane defaults.
Constructing API client wrappers where retry counts and timeouts are optional via defaults.
Creating configurable UI builders that accept optional style or behavior flags.

How to Use Default Parameter Values in Python Functions

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Functions & basics

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