Parse Input with Schemas
------------------------

In the common "web form" use case you already get parameters mapped to keys. 
That's usually the job of your web framework. However sometimes it's not that 
easy: Before you can do input validation, you need to parse the user input from
a string and convert that into a dict.

This is where ''PositionalArgumentsParsingSchema()'' might help you: This schema
takes a string and extracts several parameters from it. So you can use it to
transform ``"foo, 42"`` into ``dict(name="foo", value=42)``.

.. autoclass:: pycerberus.schemas.PositionalArgumentsParsingSchema
   :members:

This schema is used for example in `pymta <http://www.schwarz.eu/opensource/projects/pymta>`_.
to parse the SMTP command strings. Also I used it in my 
`OhlohWidgetsMacro <http://www.schwarz.eu/opensource/projects/ohloh_widgets_macro>`_:
Trac macros can get parameters but these are passed as a single string so the 
schema takes care of separating these arguments.


