https://github.com/thesis/optional_import

Optional imports in Python
https://github.com/thesis/optional_import

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Optional imports in Python

• Host: GitHub
• URL: https://github.com/thesis/optional_import
• Owner: thesis
• License: mit
• Created: 2014-06-17T22:39:05.000Z (about 12 years ago)
• Default Branch: master
• Last Pushed: 2014-06-19T03:39:24.000Z (about 12 years ago)
• Last Synced: 2026-01-13T17:25:18.874Z (6 months ago)
• Language: Python
• Size: 234 KB
• Stars: 1
• Watchers: 5
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.rst
  • License: LICENSE

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README

          
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optional_import

===============

Optional imports in Python

.. pypi - Everything below this line goes into the description for PyPI.

Usage

-----

This library contains only the context manager ``optional_import``:

.. code:: python

    >>> from optional_import import optional_import

A successful import works as usual:

.. code:: python

    >>> with optional_import():

    ...     import collections

    >>> type(collections)

    

If the import does not exist, ``optional_import`` suppresses the

``ImportError`` that would otherwise be raised.

.. code:: python

    >>> import unicorns

    Traceback (most recent call last):

      ...

    ImportError: No module named unicorns

    >>> with optional_import():

    ...     import unicorns

    >>> unicorns

    Traceback (most recent call last):

      ...

    NameError: name 'unicorns' is not defined

Example: Django local settings

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A common pattern in Django is to put default settings in ``settings.py``,

put optional site-specific settings in ``settings_local.py``, and import

``*`` from the local settings file if it exists.

.. code:: python

    with optional_import():

        from .settings_local import *

Why not just catch ``ImportError``?

-----------------------------------

Optional imports can almost be achieved simply by catching ``ImportError``:

.. code:: python

    try:

        import foo

    except ImportError:

        pass

But this approach introduces a problem: If ``foo`` exists but raises

``ImportError``, we want that error to be raised, but instead it is

swallowed by the ``except`` clause.

With ``optional_import``, the error is raised as desired. In the following

example, the ``bad`` module tries to import a nonexistent package ``unicorns``:

.. code:: python

    >>> with optional_import():

    ...     import bad

    Traceback (most recent call last):

      ...

    ImportError: No module named unicorns