.. _python_booster:

================
Python booster
================

`This page
<http://wordaligned.org/articles/essential-python-reading-list>`_ will
give you a warm feeling in your stomach.

Non-Basic Python features
-------------------------

Theano doesn't use your grandfather's python.

  * properties

    a specific attribute that has get and set methods which python automatically invokes.

    See [http://www.python.org/doc/newstyle/ New style classes].
  * static methods vs. class methods vs. instance methods
  * Decorators:

    .. code-block:: python

      @f
      def g():
        ...

    runs function ``f`` before each invocation of ``g``.
    See `PEP 0318 <http://www.python.org/dev/peps/pep-0318/>`_.
    ``staticmethod`` is a specific decorator, since python 2.2
  *  ``__metaclass__`` is kinda like a decorator for classes. It runs the metaclass __init__ after the class is defined
  * ``setattr`` + ``getattr`` + ``hasattr``
  * ``*args`` is a tuple like argv in C++, ``**kwargs`` is a keyword args version
  * ``pass`` is no-op.
  * functions (function objects) can have attributes too. This technique
    is often used to define a function's error messages.

    .. code-block:: python

        def f(): return f.a
        f.a = 5
        f() # returns 5

  * Warning about mutual imports:

    * script a.py file defined a class A.
    * script a.py imported file b.py
    * file b.py imported a, and instantiated a.A()
    * script a.py instantiated its own A(), and passed it to a function in b.py
    * that function saw its argument as being of type __main__.A, not a.A.

    Incidentally, this behaviour is one of the big reasons to put autotests in
    different files from the classes they test!

    If all the test cases were put into <file>.py directly, then during the test
    cases, all <file>.py classes instantiated by unit tests would have type
    ``__main__.<classname>``, instead of type ``<file>.<classname>``.  This should never
    happen under normal usage, and can cause problems (like the one you are/were
    experiencing).

