Partial Functions in Python

Note#82

notes
Published

2023-05-02

Partial Functions in Python

A partial function is derived from an existing function by pre-filling (or “fixing”) some of its arguments with specific values. This creates a new function that behaves like the original but with fewer arguments to supply. In Python, you create them using functools.partial(func, *args, **kwargs).

Core Uses & Benefits

Partial functions enhance code reusability by allowing you to create specialized versions of general functions. They improve readability by giving these pre-configured functions meaningful names. They are also valuable for customizing callbacks by pre-supplying necessary arguments while still matching an expected function signature.

Examples

Fixing a positional argument

import functools
def add(x, y): return x + y
add_three = functools.partial(add, 3)  # x is fixed to 3
print(add_three(5))  # Output: 8

Configuring specialized functions by fixing keyword arguments

import functools
def send_notification(message, recipient, channel):
    print(f"Sending to {recipient} via {channel}: {message}")

# Pre-configure notifiers for different channels
email_notifier = functools.partial(send_notification, channel="email")
sms_notifier = functools.partial(send_notification, channel="sms")

# Later, use the specialized notifiers
email_notifier(recipient="user@example.com", message="Your order has shipped!")
# Output: Sending to user@example.com via email: Your order has shipped!
sms_notifier(recipient="+1234567890", message="Meeting reminder at 2 PM.")
# Output: Sending to +1234567890 via sms: Meeting reminder at 2 PM.