Partial Functions vs Closures in Python

Zettel#83

zettelkasten
Published

2023-05-02

Partial Functions

  • Derived from another function by fixing some of its arguments
  • Reduces the number of required arguments to call the new function
  • Created using the partial function from the functools module
  • Mainly used for creating specialized versions of more general functions or preconfiguring a function with some arguments for later use

Example

import functools

def add(x, y):
    return x + y

add_five = functools.partial(add, 5)

result = add_five(3)
print(result)

Closures

  • Nested functions that capture and remember values of variables from the enclosing function’s scope
  • Created using nested functions and the nonlocal keyword
  • Provide more flexibility by capturing multiple variables from the enclosing scope and having access to the entire scope, not just the fixed arguments
  • Used to create functions with behavior that depends on data not passed as arguments and to define stateful functions

Example

def make_adder(x):
    def add(y):
        return x + y
    return add

add_five = make_adder(5)

result = add_five(3)
print(result)

Key Differences

  1. Creation: Partial functions use the functools.partial function, while closures use nested functions and captured variables
  2. Flexibility: Closures offer more flexibility due to access to the entire enclosing scope, while partial functions focus on fixing arguments
  3. Intent: Partial functions specialize or preconfigure functions, while closures create functions with behavior dependent on non-argument data and can define stateful functions