.. _redefined-builtin:

redefined-builtin / W0622
=========================

**Message emitted:**

``Redefining built-in %r``

**Description:**

*Used when a variable or function override a built-in.*

**Problematic code:**

.. literalinclude:: /data/messages/r/redefined-builtin/bad.py
   :language: python

**Correct code:**

.. literalinclude:: /data/messages/r/redefined-builtin/good.py
   :language: python


**Additional details:**

The :ref:`allowed-redefined-builtins <variables-options>` option lets you specify names that are permitted to shadow built-ins.

However, this option is not effective for redefinitions at the module level or for global variables. For example:

Module-Level Redefinitions::

    # module_level_redefine.py
    id = 1  # Shadows the built-in `id`

Global Variable Redefinitions::

    # global_variable_redefine.py
    def my_func():
        global len
        len = 1  # Shadows the built-in `len`

Rationale:

Shadowing built-ins at the global scope is discouraged because it obscures their behavior
throughout the entire module, increasing the risk of subtle bugs when the built-in is needed elsewhere.
In contrast, local redefinitions are acceptable as their impact is confined to a specific scope,
reducing unintended side effects and simplifying debugging.



Created by the `variables <https://github.com/pylint-dev/pylint/blob/main/pylint/checkers/variables.py>`__ checker.