Home Backend Development Python Tutorial Why Does `is` Fail to Compare Methods in Python, But Works for Functions?

Why Does `is` Fail to Compare Methods in Python, But Works for Functions?

Nov 02, 2024 pm 06:35 PM

  Why Does `is` Fail to Compare Methods in Python, But Works for Functions?

Method Equality in Python: Unraveling the Reference Inequality Enigma

In Python, methods and functions exhibit a curious difference: while functions exhibit reference equality, methods do not. This can lead to unexpected bugs, particularly when relying on the is operator to compare methods.

Why Reference Equality Eludes Methods

Unlike functions, which are static entities, method objects are created dynamically each time they are accessed. This is because methods act as descriptors, returning a new method object when their .__get__ method is invoked. For instance, in the example provided:

class What:
    def meth(self):
        pass
Copy after login

The assignment What.meth returns a function object, which is different from the bound method object created later when inst.meth is called. This explains why What.meth is What.meth evaluates to False.

Is Equality in Python 3.8

In Python versions 3.8 and later, an alternative approach is available: using == for equality testing. Two methods are considered equal if their .__self__ and .__func__ attributes are identical objects, indicating that they wrap the same function and are bound to the same instance.

For Functions __and Unbound Methods

Regardless of Python version, functions and unbound methods (in Python 2) can be compared using the is operator, as they both represent the same underlying function reference.

Test for Underlying Function

If the requirement is to check if two methods represent the same underlying function, the .__func__ attribute can be compared:

if What().meth.__func__ == What().meth.__func__:
    print("Methods represent the same function")
Copy after login

This approach provides consistent and reliable equality checks for methods and functions, regardless of their binding status or Python version.

The above is the detailed content of Why Does `is` Fail to Compare Methods in Python, But Works for Functions?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot Article Tags

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

How Do I Use Beautiful Soup to Parse HTML? How Do I Use Beautiful Soup to Parse HTML? Mar 10, 2025 pm 06:54 PM

How Do I Use Beautiful Soup to Parse HTML?

How to Download Files in Python How to Download Files in Python Mar 01, 2025 am 10:03 AM

How to Download Files in Python

Image Filtering in Python Image Filtering in Python Mar 03, 2025 am 09:44 AM

Image Filtering in Python

How to Use Python to Find the Zipf Distribution of a Text File How to Use Python to Find the Zipf Distribution of a Text File Mar 05, 2025 am 09:58 AM

How to Use Python to Find the Zipf Distribution of a Text File

How to Work With PDF Documents Using Python How to Work With PDF Documents Using Python Mar 02, 2025 am 09:54 AM

How to Work With PDF Documents Using Python

How to Cache Using Redis in Django Applications How to Cache Using Redis in Django Applications Mar 02, 2025 am 10:10 AM

How to Cache Using Redis in Django Applications

How to Perform Deep Learning with TensorFlow or PyTorch? How to Perform Deep Learning with TensorFlow or PyTorch? Mar 10, 2025 pm 06:52 PM

How to Perform Deep Learning with TensorFlow or PyTorch?

How to Implement Your Own Data Structure in Python How to Implement Your Own Data Structure in Python Mar 03, 2025 am 09:28 AM

How to Implement Your Own Data Structure in Python

See all articles