Syntax for optional parameters not correct

[timobrembeck]

In your tutorial, you suggest using , optional after the parameter type to denote that a parameter is optional.
However, according to the following sources, this is not the official syntax for sphinx/reStructuredText docstrings:

• Sphinx documentation
• Read the Docs theme documentation
• Discussion on Google Groups

Moreover, Sphinx procudes a warning when used in nit-picky mode:

WARNING: py:class reference target not found: optional

Thus, I suggest removing this syntax from the tutorial. I'm sorry if I missed any important resources.