Learn Partial functions Python programming

By Bernard Aybout (Virii8) April 15, 2018

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Lesson: Learn Partial functions Python programming

Introduction

Partial functions in Python are a powerful tool that allows you to fix a certain number of arguments of a function and generate a new function. This is particularly useful when you need to simplify function calls by presetting some arguments.

What You Need

To create partial functions, you’ll need the partial function from the functools library.

from functools import partial

How Partial Functions Work

Partial functions derive a function with fewer parameters by fixing some of the original function’s parameters. This means you can call the resulting function with fewer arguments, which can make your code more concise and readable.

Example 1: Basic Usage

Consider a simple function that multiplies two numbers:

from functools import partial

def multiply(x, y):
    return x * y

# Create a new function that multiplies by 2
dbl = partial(multiply, 2)
print(dbl(4))  # Output: 8

In this example, dbl is a new function derived from multiply with the first parameter fixed at 2. When dbl(4) is called, it multiplies 2 by 4 to return 8.

Important Note – Learn Partial functions Python programming

When using partial, the default values replace variables starting from the left. For example, in dbl = partial(multiply, 2), the 2 replaces x. This might not make a difference in simple examples, but it’s crucial in more complex functions.

Example 2: More Complex Usage

Here’s a more complex example:

from functools import partial

def func(u, v, w, x):
    return u*4 + v*3 + w*2 + x

# Create a partial function with the first three parameters fixed
p = partial(func, 5, 6, 7)
print(p(8))  # Output: 60

In this example, p is a new function where u, v, and w are fixed to 5, 6, and 7 respectively. When p(8) is called, it computes 5*4 + 6*3 + 7*2 + 8, resulting in 60.

Exercise – Learn Partial functions Python programming

Now it’s your turn to practice creating partial functions. Follow the instructions below to complete the exercise.

Instructions

Define a function func with four parameters: u, v, w, and x.
Use the partial function to create a new function by fixing the first three parameters of func to 5, 6, and 7.
Call the new partial function with a single argument so that the output is 60.

Code to Start

from functools import partial

def func(u, v, w, x):
    return u*4 + v*3 + w*2 + x

# Create your partial function here

# Print the result here

Assignment Answer Key

Here’s the solution for the exercise:

# This is the answer code. Try coding the answer yourself first.
from functools import partial

def func(u, v, w, x):
    return u*4 + v*3 + w*2 + x

p = partial(func, 5, 6, 7)
print(p(8))  # Output: 60

You can use an online Python compiler like Trinket.io to test your code and see the results instantly.

Summary – Learn Partial functions Python programming

Partial functions are a handy feature in Python that allow you to fix certain arguments of a function and create a new function with fewer parameters. This can simplify your code and make function calls more intuitive. Practice creating partial functions to become more comfortable with this powerful tool!

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Partial Functions in Python – Functools Tutorial

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