Added documentation on how to contribute new graphs

docs/contributing.rst

@@ -3,7 +3,7 @@ Contributing
 ============
 
 
-Github
+GitHub
 ======
 
 Submit your bug reports and feature requests to the `github bug tracker <http://github.com/Kozea/pygal/issues>`_.
@@ -18,7 +18,7 @@ The pygal code tries to respect the `pep8 <https://www.python.org/dev/peps/pep-0
 Testing
 =======
 
-Before submiting a pull request, please check that all tests still pass.
+Before submitting a pull request, please check that all tests still pass.
 
 
 To do this install ``py.test`` and them run ``py.test`` in the root of your pygal clone:
@@ -36,3 +36,45 @@ Continuous Integration
 
 The current build status can be seen at our `ymci <https://ymci.kozea.fr/project/view/12>`_
 
+
+Contributing a New Graph Visualization
+======================================
+
+* Fork the pygal repository on GitHub
+* Clone your own fork: ``git clone [email protected]:<Your_GH_User>/pygal.git``
+* ``cd pygal``
+* Create a virtual environment for development: ``python -m venv .pygal_dev``
+* Activate the virtual environment ``source .pygal_dev/bin/activate`` (see `PyPA documentation <https://setuptools.pypa.io/en/latest/userguide/development_mode.html>` for how to do that on Windows)
+* Install pygal in development mode into the virtual environment ``pip install --editable ".[test]"``
+
+The following steps are illustrated on reusing an existing graph, the Pie Graph. For your new visualization, adapt the names, the respective test code, and the actual visualization code accordingly.
+
+* Add a test ``touch pygal/test/test_mypie.py``. For example, add the following code to it
+
+.. code-block:: python
+
+from pygal import MyPie
+
+def test_donut():
+ """Test a donut pie chart"""
+ chart = MyPie(inner_radius=.3, pretty_print=True)
+ chart.title = 'Browser usage in February 2012 (in %)'
+ chart.add('IE', 19.5)
+ chart.add('Firefox', 36.6)
+ chart.add('Chrome', 36.3)
+ chart.add('Safari', 4.5)
+ chart.add('Opera', 2.3)
+ chart.render_to_file('/tmp/chart.svg')
+ assert chart.render()
+
+
+
+* Create a new file for your new graph visualization: ``touch pygal/graph/my_viz.py``. (For this example: ``cp pygal/graph/pie.py pygal/graph/mypie.py``.)
+* Add an import for your new visualization class to the ``__init__.py`` module. For this example, add ``from pygal.graph.mypie import MyPie`` to the block of imports at the top of this file.
+* To manually test your new visualization: ``pytest pygal/test/test_mypie.py``.
+* After the test completes, inspect the file that it generated (e.g., via ``open /tmp/chart.svg``) if it looks as intended.
+
+
+Now, edit the code for the visualization and its respective test.
+Once your visualization works as intended run the entire test suite as described above.
+Thereafter, send a pull-request to the main branch of the original repository (``Kozea/pygal``).