Python booster

This page 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:

    @f
def g():
  ...

    runs function f before each invocation of g. See 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.

    >>> def f(): return f.a
>>> f.a = 5
>>> f()
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).