E. Missing Features

Most of the CLIPS API is implemented in PyCLIPS. The lower level interface (which directly maps CLIPS exposed functions as described in Clips Reference Guide Vol. II: Advanced Programming Guide) can be accessed using the clips._clips submodule. Almost all the functions defined here have a counterpart in the CLIPS API, and a combined use of documentation strings and Clips Reference Guide Vol. II: Advanced Programming Guide itself can allow you to directly manipulate the CLIPS subsystem as you would have done by embedding it in a C program. However, there are some functions that appear in dir(clips._clips) but, when called, issue an error:

>>> clips._clips.addClearFunction()
Traceback (most recent call last):
  File "<pyshell#46>", line 1, in ?
    clips._clips.addClearFunction()
ClipsError: C98: unimplemented feature/function

and in fact, even their documentation string reports

>>> print clips._clips.addClearFunction.__doc__
unimplemented feature/function

even if the name of the function is defined and is a callable.

A list of such functions follows:

Function Type
addClearFunction execution hook
addPeriodicFunction execution hook
addResetFunction execution hook
removeClearFunction execution hook
removePeriodicFunction execution hook
removeResetFunction execution hook
addRunFunction execution hook
removeRunFunction execution hook
decrementFactCount reference count handler
incrementFactCount reference count handler
decrementInstanceCount reference count handler
incrementInstanceCount reference count handler
setOutOfMemoryFunction memory handler hook
addEnvironmentCleanupFunction execution hook
allocateEnvironmentData memory handler
deallocateEnvironmentData memory handler
destroyEnvironment environment destructor
getEnvironmentData memory handler

The description of these functions is outside the scope of this guide, and can be found in Clips Reference Guide Vol. II: Advanced Programming Guide of CLIPS. It is not likely that these functions will be implemented even in future versions of PyCLIPS since Python programmers are usually not interested in dealing with low level memory handling (which is the primary use of the memory oriented functions), and tasks like reference count handling are performed directly by Python itself (for Python objects which shadow CLIPS entities) and by the low level PyCLIPS submodule. Also, the functions referred to above as execution hooks often have to deal with CLIPS internal structures at a very low level, so they would be of no use in a Python program.

Other API functions, which are used internally by PyCLIPS (for instance the InitializeEnvironment() C function), are not implemented in the module.

Note: Some of the features (either in current and possibly in further versions of PyCLIPS) may depend on the version of CLIPS that is used to compile the module. Using the most recent stable version of CLIPS is recommended in order to enable all PyCLIPS features. Features that are excluded from the module because of this reason will issue an exception, in which the exception text reports the following: "C97: higher engine version required". Moreover, the CLIPS engine version may affect the behaviour of some functions. Please consider reading the documentation related to the used CLIPS version when a function does not behave as expected.