Installing Python Modules

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2.4 How installation works

After the build command runs (whether you run it explicitly, or the install command does it for you), the work of the install command is relatively simple: all it has to do is copy everything under build/lib (or build/lib.plat) to your chosen installation directory.

If you don't choose an installation directory--i.e., if you just run setup.py install--then the install command installs to the standard location for third-party Python modules. This location varies by platform and by how you built/installed Python itself. On Unix and Mac OS, it also depends on whether the module distribution being installed is pure Python or contains extensions (``non-pure''):

Platform	Standard installation location	Default value	Notes
Unix (pure)	prefix/lib/python2.0/site-packages	/usr/local/lib/python2.0/site-packages	(1)
Unix (non-pure)	exec-prefix/lib/python2.0/site-packages	/usr/local/lib/python2.0/site-packages	(1)
Windows	prefix	C:\Python	(2)
Mac OS (pure)	prefix:Lib	Python:Lib ** ??? **
Mac OS (non-pure)	prefix:Mac:PlugIns	Python:Mac:PlugIns** ??? **

Notes:

(1)

Most Linux distributions include Python as a standard part of the system, so prefix and exec-prefix are usually both /usr on Linux. If you build Python yourself on Linux (or any Unix-like system), the default prefix and exec-prefix are /usr/local.

(2)

The default installation directory on Windows was C:\Program Files\Python under Python 1.6a1, 1.5.2, and earlier.

prefix and exec-prefix stand for the directories that Python is installed to, and where it finds its libraries at run-time. They are always the same under Windows and Mac OS, and very often the same under Unix. You can find out what your Python installation uses for prefix and exec-prefix by running Python in interactive mode and typing a few simple commands. Under Unix, just type python at the shell prompt; under Windows, run ``Python 2.0 (interpreter)'' ** right? **; under Mac OS, ** ??? **. Once the interpreter is started, you type Python code at the "»> " prompt. For example, on my Linux system, I type the three Python statements shown below, and get the output as shown, to find out my prefix and exec-prefix:

Python 1.5.2 (#1, Apr 18 1999, 16:03:16)  [GCC pgcc-2.91.60 19981201 (egcs-1.1.1  on linux2
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>> import sys
>>> sys.prefix
'/usr'
>>> sys.exec_prefix
'/usr'

If you don't want to install to the standard location, or if you don't have permission to write there, then you need to read about alternate installations in the next section.

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Installing Python Modules

Previous: 2.3 How building works Up: 2 Standard Build and Next: 3 Building Extensions: Tips