Deprecation in Python

It’s always a good practice to deprecate functions, methods or classes before removing or changing something.

Features are deprecated rather than immediately removed, to provide backward compatibility, and to give programmers time to bring affected code into compliance with the new standard.


It permits to perform changes and to clean code—because it’s always necessary to make things evolve—while avoiding breaking things.

In Java there is a built-in annotation for that @Deprecated. However in Python there is no such a feature.

But as you may know, if something is missing, someone with the same concerns has already built it. There is several implementations, I’ve chosen Deprecated since

  • it’s very simple and raises a simple warning—more on that later—that is printed at runtime. In fact my first need was to print this warning clearly in Jupyter notebooks,
  • it provides a very convenient way to deprecate things through a decorator.


$ pip install deprecated

Deprecate things

from deprecated import deprecated

@deprecated(reason="use new_function")
def old_function():
    print("I'm old now I want to retire...")

def new_function():
    print("I'm ready to conquer the world!")

>>> old_function()

# __main__:1: DeprecationWarning: Call to deprecated function 
# (or staticmethod) old_function. (use new_function)
# I'm old now I want to retire...

How it works

It uses a Python standard library called warnings1.

Warning messages are typically issued in situations where it is useful to alert the user of some condition in a program, where that condition (normally) doesn’t warrant raising an exception and terminating the program. For example, one might want to issue a warning when a program uses an obsolete module.

They are managed as Exception and a more precisely by raising a DeprecationWarning printed to the sys.stderr—and so deprecation messages appear clearly in red in Jupyter notebooks.

Base class for warnings about deprecated features when those warnings are intended for other Python developers.

  1. warnings — Warning control ↩︎