Usage
=====

Roles and Directives
--------------------

.. rst:role:: cite

   Create a citation to a bibliographic entry. For example:

   .. code-block:: rest

      See :cite:`1987:nelson` for an introduction to non-standard analysis.

   which would be equivalent to the following LaTeX code:

   .. code-block:: latex

      See \cite{1987:nelson} for an introduction to non-standard analysis.

.. rst:directive:: .. bibliography:: refs.bib [...]

   Create bibliography for all cited references. The ``all`` flag
   forces all references to be included (equivalent to ``\nocite{*}``
   in LaTeX). The ``notcited`` flag causes all references that were
   not cited to be included. The ``cited`` flag is recognized as well
   but is entirely optional. For example:

   .. code-block:: rest

     .. rubric:: References

     .. bibliography:: refs.bib
        :cited:

   which would be roughly equivalent to the following LaTeX code:

   .. code-block:: latex

      \begin{thebibliography}{1}
        \bibitem{1987:nelson}
        Edward~Nelson
        \newblock {\em Radically Elementary Probability Theory}.
        \newblock Princeton University Press, 1987.
      \end{thebibliography}

   Note that, unlike LaTeX, the :rst:dir:`bibliography` directive does
   not generate a default section title.

   .. warning::

      Sphinx may not be able to create an entry for :rst:role:`cite` keys
      when your :rst:dir:`bibliography` directive
      resides in a different document;
      see :ref:`issue-unresolved-citations`
      for more information and workarounds.

   You can also pick a bibliography style, using the ``style`` option.
   This is not yet quite as useful, as only ``plain`` and ``unsrt``
   are supported.
   The ``plain`` style is the default.

   .. code-block:: rest

     .. bibliography:: refs.bib
        :style: unsrt

   All citations have numbered labels, as in the ``plain`` LaTeX
   bibliography style, regardless of the style chosen. This limitation
   might be lifted in a future version.

   .. warning::

      Sphinx will attempt to resolve references to the bibliography
      across all documents, so you must take care that no citation key
      is included more than once.

   You can also set the encoding of the bibliography files, using the
   ``encoding`` option.

   .. code-block:: rest

     .. bibliography:: refs.bib
        :encoding: latex+latin

   Note that, usually, you want to prepend your encoding with
   ``latex+``, in order to convert LaTeX control characters to unicode
   characters (for instance, to convert ``\'e`` into ``é``). The latex
   codec is invoked by default, for your convenience. Be sure to write
   ``\%`` when you intend to format a percent sign.

.. XXX not documenting disable-curly-bracket-strip for now; might remove it

   Finally, curly brackets are automatically removed when the bib file
   is parsed. Usually, this is what you want. If you desire to disable
   this behaviour, use the ``disable-curly-bracket-strip`` option:

   .. code-block:: rest

     .. bibliography:: refs.bib
        :disable-curly-bracket-strip:

Advanced Features
-----------------

Bullet Lists and Enumerated Lists
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 0.2.4

You can change the type of list used for rendering the
bibliography. By default, a paragraph of standard citations is
generated. However, instead, you can also generate a bullet list,
or an enumerated list.

.. code-block:: rest

   .. bibliography:: refs1.bib
      :list: bullet
      :all:

   .. bibliography:: refs2.bib
      :list: enumerated
      :all:

Note that citations to these types of bibliography lists will not
be resolved.

For enumerated lists, you can also specify the type (default is
``arabic``), and the start of the sequence (default is ``1``).

.. code-block:: rest

   .. bibliography:: refs2.bib
      :list: enumerated
      :enumtype: upperroman
      :start: 3
      :all:

The enumtype can be any of
``arabic`` (1, 2, 3, ...),
``loweralpha`` (a, b, c, ...),
``upperalpha`` (A, B, C, ...),
``lowerroman`` (i, ii, iii, ...), or
``upperroman`` (I, II, III, ...).

The start can be any positive integer (1, 2, 3, ...) or
``continue`` if you wish the enumeration to continue from the last
:rst:dir:`bibliography` directive.
This is helpful if you split up your bibliography but
still want to enumerate the entries continuously.

Label Prefixing
~~~~~~~~~~~~~~~

.. versionadded:: 0.2.5

If you have multiple bibliographies, and experience duplicate labels,
use the ``labelprefix`` option.

.. code-block:: rest

   .. rubric:: References

   .. bibliography:: refs.bib
      :cited:
      :labelprefix: A

   .. rubric:: Further reading

   .. bibliography:: refs.bib
      :notcited:
      :labelprefix: B

Filtering
~~~~~~~~~

.. versionadded:: 0.2.7

Whilst the ``cited``, ``all``, and ``notcited`` options
will cover many use cases,
sometimes more advanced selection of bibliographic entries is desired.
For this purpose, you can use the ``filter`` option:

.. code-block:: rest

   .. bibliography:: refs.bib
      :list: bullet
      :filter: author % "Einstein"

The string specified in the filter option must be a valid Python
expression.

.. note::

   The expression is parsed using :func:`ast.parse`
   and then evaluated using an :class:`ast.NodeVisitor`,
   so it should be reasonably safe against malicious code.

The filter expression supports:

* The boolean operators ``and`` and ``or``.

* The unary operator ``not``.

* Binary comparison ``==``, ``<=``, ``<``, ``>=``, and ``>``.

* Regular expression matching using the ``%`` operator, where the left
  hand side is the string to be matched, and the right hand side is
  the regular expression. Matching is case insensitive. For example:

    .. code-block:: rest

       .. bibliography:: refs.bib
          :list: bullet
          :filter: title % "relativity"

  would include all entries that have the word "relativity" in the title.

  .. note::

     The implementation uses :func:`re.search`.

* Single and double quoted strings, such as ``'hello'`` or ``"world"``.

* Various identifiers, such as:

  - ``type`` is the entry type, as a lower case string
    (i.e. ``"inproceedings"``).

  - ``key`` is the entry key, as a lower case string
    (this is because keys are considered case insensitive).

  - ``cited`` evaluates to ``True`` if the entry was cited in the document,
    and to ``False`` otherwise.

  - ``True`` and ``False``.

  - ``author`` is the entry string of authors
    in standard format (last, first), separated by "and".

  - ``editor`` is similar to ``author`` but for editors.

  - Any other (lower case) identifier evaluates to a string
    containing the value of
    the correspondingly named field, such as
    ``title``, ``publisher``, ``year``, and so on.
    If the item is missing in the entry
    then it evaluates to the empty string.
    Here is an example of how one would typically write an expression
    to filter on an optional field:

    .. code-block:: rest

       .. bibliography:: refs.bib
          :list: bullet
          :filter: cited and year and (year <= "2003")

    which would include all cited entries that have a year
    that is less or equal than 2003; any entries that do not
    specify a year would be omitted.

Custom Formatting, Sorting, and Labelling
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

:mod:`pybtex` provides a very powerful way to create and register new
styles, using setuptools entry points,
as documented here: http://pybtex.sourceforge.net/plugins.html

One way to leverage the pybtex plugin system from within Sphinx,
is to create a package stub with the desired entry points
(if you know of a simpler way, please let me know!).
Start with laying out your documentation folder as follows::

   conf.py
   index.rst
   plugins/plugins.py
   plugins/setup.py
   plugins/plugins.egg-info/dependency_links.txt
   plugins/plugins.egg-info/entry_points.txt
   plugins/plugins.egg-info/PKG-INFO
   plugins/plugins.egg-info/SOURCES.txt
   plugins/plugins.egg-info/top_level.txt
   ...

The egg-info files are generated by running ``python setup.py egg_info``
You do not actually need to install the plugins package.
Our ``conf.py`` will load it, and its entry points,
using the :mod:`pkg_resources` module,
through the following code (along with the rest of your configuration)::

  import pkg_resources
  for dist in pkg_resources.find_distributions("plugins/"):
      pkg_resources.working_set.add(dist)

The ``plugins/setup.py`` file,
which is only used to generate the egg-info files,
should be::

  from setuptools import setup

  setup(
      name='plugins',
      version='0.1.0',
      entry_points={
          'pybtex.style.formatting': [
              'mystyle = plugins:MyStyle',
              ]
          },
      py_modules=['plugins']
      )

The actual custom style(s) reside in ``plugins/plugins.py``; for instance:

.. code-block:: python

  from pybtex.style.formatting.unsrt import Style as UnsrtStyle
  from pybtex.style.template import toplevel # ... and anything else needed

  class MyStyle(UnsrtStyle):
      name = 'mystyle'
      default_name_style = 'lastfirst' # 'lastfirst' or 'plain'
      default_label_style = 'number' # 'number' or 'alpha'
      default_sorting_style = 'author_year_title' # 'none' or 'author_year_title'

      def format_XXX(self, e):
          template = toplevel [
              # etc.
          ]
          return template.format_data(e)

The formatting code uses a very intuitive template engine.
The source code for ``unsrt`` provides many great examples:
http://bazaar.launchpad.net/~pybtex-devs/pybtex/trunk/view/head:/pybtex/style/formatting/unsrt.py

The above example only demonstrates a custom formatting style plugin.
It is also possible to register custom author/editor naming plugins
(using the ``pybtex.style.names`` group)
and labelling plugins
(using the ``pybtex.style.labels`` group).

.. note::

   There is no documented entry point for sorting plugins,
   but the ``pybtex.style.sorting`` group appears to work.

An minimal example is available here:
https://github.com/mcmtroffaes/sphinxcontrib-bibtex/tree/develop/test/custom_style

Known Issues and Workarounds
----------------------------

Tinkerer
~~~~~~~~

To use the bibtex extension with `Tinkerer <http://www.tinkerer.me/>`_,
be sure to specify the bibtex extension first in your ``conf.py`` file::

    extensions = ['sphinxcontrib.bibtex', 'tinkerer.ext.blog', 'tinkerer.ext.disqus']

Encoding: Percent Signs
~~~~~~~~~~~~~~~~~~~~~~~

When using the LaTeX codec (which is by default), be sure to write
``\%`` for percent signs at all times (unless your file contains a
genuine comment), otherwise the bibtex lexer will ignore the remainder
of the line.

If you don't want any LaTeX symbols to be reinterpreted as unicode,
use the option ``:encoding: utf`` (without the ``latex+`` prefix).

.. _issue-unresolved-citations:

Unresolved Citations Across Documents
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you cite something that has its bibliography in another document,
then, at the moment, the extension may, or may not, realise that it
has to add this citation.
There are a few ways to work around this problem:

* Use the option ``:all:`` in the :rst:dir:`bibliography`
  directive (which will simply cause all entries to be included).

* Ensure that the :rst:dir:`bibliography` directive is processed after
  all :rst:role:`cite`\ s. Sphinx appears to process files in an
  alphabetical manner. For instance, in case you have only one file
  containing a :rst:dir:`bibliography` directive, simply name that
  file :file:`zreferences.rst`.

Hopefully, this limitation can be lifted in a future release.

KeyError When Using ``:style: plain``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When using the ``plain`` style, or any style that sorts entries, pybtex
may raise ``KeyError: 'author'`` for entries that have no author. A
patch has been submitted upstream:

https://code.launchpad.net/~matthias-troffaes/pybtex/sorting-bugfix

Duplicate Labels When Using ``:style: plain``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

With ``:style: plain``, labels are numerical,
restarting at ``[1]`` for each :rst:dir:`bibliography` directive.
Consequently, when inserting multiple :rst:dir:`bibliography` directives
with ``:style: plain``,
you are bound to get duplicate labels for entries.
There are a few ways to work around this problem:

* Use a single bibliography directive for all your references.

* Use the ``labelprefix`` option, as documented above.

* Use a style that has non-numerical labelling.
  Unfortunately, pybtex does not yet support such styles.
  A patch for non-numerical styles, such as ``:style: alpha``,
  has been submitted upstream:

  https://code.launchpad.net/~matthias-troffaes/pybtex/label-alpha

  When this becomes part of pybtex,
  the plan is to change the default citation style to ``:style: alpha``,
  as this style is also more in line with
  how citations are usually labelled in Sphinx.