Caches the *filtered* file `filename` with `key` until the file is
modified.

:param key: the cache key
:param filename: the file to cache
:param filter: is the function used for filtering. Normally `filename` is a
    .py file and `filter` is a function that bytecode compiles the file.
    In this way the bytecode compiled file is cached. (Default = None)

This is used on Google App Engine since pyc files cannot be saved.

In apps, instead of importing a local module
(in applications/app/modules) with::

   import a.b.c as d

you should do::

   d = local_import('a.b.c')

or (to force a reload):

   d = local_import('a.b.c', reload=True)

This prevents conflict between applications and un-necessary execs.
It can be used to import any module, including regular Python modules.

Read the code inside a bytecode compiled file if the MAGIC number is compatible

:returns: a code object

Runs the controller.function() (for the app specified by the current folder). It tries pre-compiled controller_function.pyc first before compiling it.

Executes the view for the requested action. The view is the one specified in `response.view` or determined by the url or `view/generic.extension` It tries the pre-compiled views_controller_function.pyc before compiling it.

Example:

   >>> import traceback, types
   >>> environment={'x':1}
   >>> open('a.py', 'w').write('print 1/x')
   >>> save_pyc('a.py')
   >>> os.unlink('a.py')
   >>> if type(read_pyc('a.pyc'))==types.CodeType: print 'code'
   code
   >>> exec read_pyc('a.pyc') in environment
   1

TEST_CODE

Value:

''' def _TEST(): import doctest, sys, cStringIO, types, cgi, gluon.fileutils if not gluon.fileutils.check_credentials(request): raise HTTP(400, web2py_error=\'invalid credentials\') stdout = sys.stdout html = \'<h2>Testing controller "%s.py" ... done.</h2><br/>\\n\' \ \ ...