Python PendingDeprecationWarning – Tutorial with Examples

In Python, developers often use various third-party libraries to implement specific functionality. As libraries are developed further, various issues may arise that result in specific functions being deprecated but still in use. To give a grace period of updates from the developer’s side, Python adds pending deprecation warnings around the use of the deprecated function. These warnings are then sent to developers, highlighting that the function is deprecated and outlining that it will be removed in the forthcoming Python versions.

This tutorial will provide an understanding of the PendingDeprecationWarning, why it is used, and how users can handle these warnings. We will go through some real-life examples to help understand the Python PendingDeprecationWarning functionality.

What is PendingDeprecationWarning?

A PendingDeprecationWarning is a notice that is warning developers that a certain part of the code will be removed soon. Despite being labeled as pending, the feature is still deprecated and as such, is not recommended for use in the long term. This ensures that developers have enough time to update their code and make the necessary changes that will allow their program to function correctly without that deprecated feature.

Reasons for Using PendingDeprecationWarning

There are various reasons why PendingDeprecationWarning is used. Different developers will have their own specific reasons for using it; however, some of the most common reasons for using PendingDeprecationWarning include:

• To give the developer time to adjust their code: One of the most common reasons why PendingDeprecationWarning is used is to ensure that developers have time to adjust their code to account for the removal of any deprecated features.
• To maintain compatibility: Another primary reason why PendingDeprecationWarning is used is to maintain compatibility with older versions of Python while also allowing developers to use deprecated functions.

How to Handle PendingDeprecationWarning

Python provides several methods for handling PendingDeprecationWarning messages in terms of how they are reported to the developer. Some of the methods include:

• Ignoring PendingDeprecationWarnings: There are situations where developers may choose to ignore PendingDeprecationWarnings. One of the ways of ignoring it is by using the command-line option `-W`.
• Filtering PendingDeprecationWarnings: Developers can filter out some warning messages, which they find unnecessary, by importing the warnings module and calling the filterwarnings() function.

Examples

In this section, we will provide some examples that demonstrate how the PendingDeprecationWarning works.

Example 1:

Consider the following code snippet:

import copy_reg
  
def load_pickle(pkl_file_name):
    with open(pkl_file_name, 'rb') as file:
        return pickle.load(file)

file_name = "some_file.pkl"
obj = load_pickle(file_name)

This code will run fine in Python 2.x, but if you try running it in Python 3.x, it will give you a PendingDeprecationWarning as shown below:

PendingDeprecationWarning: The copy_reg module is deprecated, use the module <a href="https://docs.python.org/3/library/pickle.html#module-pickle">pickle</a> instead.

The basic structure of the code will remain the same, but instead of using copy_reg, we will make use of pickle, as Python specifies in the Warning message above.

Example 2:

Consider the code snippet below:

import urllib

urllib.urlopen("https://example.com")

This code will work fine in python 2.x, but if we try to run it in python 3.x, it will raise a PendingDeprecationWarning as shown below:

PendingDeprecationWarning: urllib.urlopen is deprecated - use urllib.request.urlopen() instead.

To update the code and make it work properly in Python 3.x, we need to replace it with:

import urllib.request

urllib.request.urlopen("https://example.com")

Example 3:

Consider the code snippet below:

import email.Utils

email.Utils.formatdate(localtime=True)

Trying to run this code snippet in python 3.x will raise a PendingDeprecationWarning:

PendingDeprecationWarning: the email.Utils module is deprecated and will be removed in a future release

To make it work in Python 3.x, swap the imports with:

from email import utils

utils.formatdate(localtime=True)

Conclusion

PendingDeprecationWarning is essential when a specific functionality is being removed, and developers need time to adjust their code to account for that change. While deprecated functions can continue to work correctly in earlier versions of Python, long-term use is not recommended. Knowing how to adjust code that contains pending deprecation warnings will be essential in ensuring that programs run correctly in future Python releases.

We hope this tutorial provided a fundamental understanding of the PendingDeprecationWarning in Python, reasons for using it, and how to handle its functionality. Keep practicing with different deprecation warnings to ensure that your Python code always runs correctly.