By simply importing the hou module into a regular Python shell, you can easily integrate Houdini into your existing Python-based scripts. The first time you import hou, Python will load in all of Houdini’s libraries and initialize an empty Houdini session. The hou module effectively stores a Houdini session, and you can load into that session from a hip file, inspect that file from your script, and input and output information to and from nodes in that session.

In order to import the hou module, you need to tell Python to search in $HFS/houdini/python2.7libs for Python modules. One way to accomplish this is to append this to the PYTHONPATH environment variable before starting Python, and another is to append the path to the sys.path from within Python. The following Python snippet will import the hou module into a standard Python shell, assuming that you sourced houdini_setup to set $HFS and paths.

When you import the hou module, the standard Houdini initialization scripts 123.cmd/123.py and 456.cmd/456.py will not be run. If you want these scripts to run, you must explicitly call hou.__runUserDefinedCode().

#!/usr/bin/python
def enableHouModule():
    '''Set up the environment so that "import hou" works.'''
    import sys, os

    # Importing hou will load in Houdini's libraries and initialize Houdini.
    # In turn, Houdini will load any HDK extensions written in C++.  These
    # extensions need to link against Houdini's libraries, so we need to
    # make sure that the symbols from Houdini's libraries are visible to
    # other libraries that Houdini loads.  So, we adjust Python's dlopen
    # flags before importing hou.
    if hasattr(sys, "setdlopenflags"):
        old_dlopen_flags = sys.getdlopenflags()
        import DLFCN
        sys.setdlopenflags(old_dlopen_flags | DLFCN.RTLD_GLOBAL)

    try:
        import hou
    except ImportError:
        # Add $HFS/houdini/python2.7libs to sys.path so Python can find the
        # hou module.
        sys.path.append(os.environ['HFS'] + "/houdini/python%d.%dlibs" % sys.version_info[:2])
        import hou
    finally:
        if hasattr(sys, "setdlopenflags"):
            sys.setdlopenflags(old_dlopen_flags)

enableHouModule()
import hou

# Uncomment the following line to run the 123.cmd/py and 456.cmd/py
# initialization scripts, now that hou is loaded.
# hou.__runUserDefinedCode()

When you import the hou module, Python will check out a license. By default, it will use a Houdini Batch license, and use a Houdini FX license if no batch license could be found. If you want it to use a Houdini license, you can set the HOUDINI_SCRIPT_LICENSE variable to hescape before importing the hou module. You can also set this variable from within your Python script with os.environ['HOUDINI_SCRIPT_LICENSE'] = 'hescape'.

By default, the hou module will not return the Houdini license until the Python interpreter exits. However, if you have a long running Python script and want to quickly acquire and release a license, you can call hou.releaseLicense() when you are done with the hou module. Subsequent calls into the hou module will reacquire the license. Note that Houdini’s session data and libraries will not be unloaded from memory until Python exits.

The hou module, when imported by Python or Houdini, will loop through the directories in $HOUDINI_PATH, and for each directory found, append that directory plus "/python2.7libs" to sys.path. For backward compatibility with older versions of Houdini, it will also look for the directories in $HOUDINI_PATH plus "/scripts/python". For example, you can put your Python modules in the directory $HOME/houdiniX.Y/python2.7libs and they will be in the Python search path after you import hou.