Partial Application

functools.partial

1. Fix Arguments

from functools import partial

def power(base, exponent):
    return base ** exponent

square = partial(power, exponent=2)
cube = partial(power, exponent=3)

print(square(5))  # 25
print(cube(5))    # 125

Use Cases

1. Configure Functions

from functools import partial

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

say_hello = partial(greet, "Hello")
say_hi = partial(greet, "Hi")

print(say_hello("Alice"))  # Hello, Alice!
print(say_hi("Bob"))       # Hi, Bob!

2. Callbacks

def log(level, message):
    print(f"[{level}] {message}")

info = partial(log, "INFO")
error = partial(log, "ERROR")

info("Starting")   # [INFO] Starting
error("Failed")    # [ERROR] Failed

Summary

• Fix some arguments
• Create specialized functions
• Useful for callbacks
• Built-in with functools