{"id":1066,"date":"2020-11-12T07:30:10","date_gmt":"2020-11-12T07:30:10","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=1066"},"modified":"2025-03-31T04:35:43","modified_gmt":"2025-03-31T04:35:43","slug":"python-partial-functions","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-partial-functions\/","title":{"rendered":"Python Partial Functions"},"content":{"rendered":"\n

Summary<\/strong>: In this tutorial, you’ll learn about Python partial functions and how to define partial functions using the partial function from the functools module.<\/p>\n\n\n\n

Introduction to Python partial functions #<\/a><\/h2>\n\n\n\n

The following example defines a function<\/a> that multiplies two arguments:<\/p>\n\n\n

def<\/span> multiply<\/span>(a, b)<\/span>:<\/span>\n    return<\/span> a*b<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Sometimes, you just want to multiply an argument with a specified number e.g., 2. To do that, you can reuse the multiply<\/code> function like this:<\/p>\n\n\n
def<\/span> double<\/span>(a)<\/span>:<\/span>\n    return<\/span> multiply(a,2<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The double<\/code> function returns the multiply<\/code> function. It passed the number 2 to the second argument of the multiply<\/code> function.<\/p>\n\n\n\n
The following shows how to use the double<\/code> function:<\/p>\n\n\n
result = double(10<\/span>)\nprint(result)    <\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Put it all together:<\/p>\n\n\n
def<\/span> multiply<\/span>(a, b)<\/span>:<\/span>\n    return<\/span> a*b\n\n\ndef<\/span> double<\/span>(a)<\/span>:<\/span>\n    return<\/span> multiply(a, 2<\/span>)\n\n\nresult = double(10<\/span>)\nprint(result)  # 20<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The double<\/code> function reduces the arguments of the multiply<\/code> function.<\/p>\n\n\n\n
The double<\/code> function freezes the second argument of the multiply<\/code> function, which results in a new function with a simpler signature.<\/p>\n\n\n\n
In other words, double<\/code> function reduces the complexity of the multiply<\/code> function.<\/p>\n\n\n\n
In Python, the double<\/code> function is called a partial function<\/strong>.<\/p>\n\n\n\n
In practice, you use partial functions when you want to reduce the number of arguments of a function to simplify the function’s signature.<\/p>\n\n\n\n
Since you’ll create partial functions sometimes, Python provides you with the partial<\/code> function from the functools<\/code> standard module to help you define partial functions more easily.<\/p>\n\n\n\n
Python partial function from functools module #<\/a><\/h2>\n\n\n\n
The following shows the syntax of the partial<\/code> function from the functools<\/code> module:<\/p>\n\n\n
functools.partial(fn, \/, *args, **kwargs)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
When you call the partial<\/code> object, Python calls the fn<\/code> function with the positional arguments args<\/code> and keyword arguments<\/a> kwargs<\/a><\/code>.<\/p>\n\n\n\n
The following example shows how to use the partial<\/code> function to define the double<\/code> function from the multiply<\/code> function:<\/p>\n\n\n
from<\/span> functools import<\/span> partial\n\ndef<\/span> multiply<\/span>(a, b)<\/span>:<\/span>\n    return<\/span> a*b\n\n\ndouble = partial(multiply, b=2<\/span>)\n\nresult = double(10<\/span>)\nprint(result)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
20<\/code><\/span><\/pre>\n\n\n
How it works.<\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
The partial<\/code> function returns new partial<\/code> object, which is a callable<\/a>.<\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n