Errno Module
============

.. toctree::
   :maxdepth: 1


Indices and tables
------------------

* :ref:`genindex`
* :ref:`modindex`
* :ref:`search`


Introduction
------------
It can be quite useful to have a standardized error number as part of an exception, or as the return value from your function or application. The :py:mod:`errno` module compliments this goal.

.. _section_heading-Error_Codes:

Error Codes
-----------
The :py:mod:`errno` module defines over 100 constants to describe various erroneous situations. For example

* :py:data:`errno.EPERM` - Operation not permitted

* :py:data:`errno.ENOENT` - No such file or directory

* :py:data:`errno.EIO` - IO error

* :py:data:`errno.EINVAL` - Invalid argument

* :py:data:`errno.ENOSYS` - Function not implemented


.. _section_heading-Error_Mapping:

Error Mapping
-------------
There are two types of mapping with error values that can be performed:


* Using the :py:data:`errno.errorcode` dictionary, you can go from error number, to the name of the constant that is defined for it. For example:

   >>> import errno
   >>> errno.errorcode[1]
   'EPERM'


* Using :py:func:`os.strerror`, you can go from error constant, to a string error message. For example:

   >>> import errno
   >>> import os
   >>> os.strerror(errno.EPERM)
   'Operation not permitted'