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Recommend the use of double underscore throwaway variables #156

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kennethreitz merged 1 commit into from
May 30, 2012
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Recommend the use of double underscore throwaway variables #156

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18 changes: 11 additions & 7 deletions docs/writing/style.rst
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Expand Up @@ -236,20 +236,24 @@ Create an ignored variable
~~~~~~~~~~~~~~~~~~~~~~~~~~

If you need to assign something (for instance, in :ref:`unpacking-ref`) but
will not need that variable, use ``_``:
will not need that variable, use ``__``:

.. code-block:: python

filename = 'foobar.txt'
basename, _, ext = filename.rpartition()
basename, __, ext = filename.rpartition()

.. note::

"``_``" is commonly used as an alias for the :func:`~gettext.gettext`
function. If your application uses (or may someday use) :mod:`gettext`,
you may want to avoid using ``_`` for ignored variables, as you may
accidentally shadow :func:`~gettext.gettext`.

Many Python style guides recommend the use of a single underscore "``_``"
for throwaway variables rather than the double underscore "``__``"
recommended here. The issue is that "``_``" is commonly used as an alias
for the :func:`~gettext.gettext` function, and is also used at the
interactive prompt to hold the value of the last operation. Using a
double underscore instead is just as clear and almost as convenient,
and eliminates the risk of accidentally interfering with either of
these other use cases.

Create a length-N list of the same thing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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