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Python in a Nutshell, 2nd Edition by Alex Martelli

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The python Program

The Python interpreter program is run as python (it’s named python.exe on Windows). python includes both the interpreter itself and the Python compiler, which is implicitly invoked, as needed, on imported modules. Depending on your system, the program may have to be in a directory listed in your PATH environment variable. Alternatively, as with any other program, you can give a complete pathname to it at a command (shell) prompt, or in the shell script (or .BAT file, shortcut target, etc.) that runs it.[1] On Windows, you can also use Start → Programs → Python 2.4 → Python (command line).

Environment Variables

Besides PATH, other environment variables affect the python program. Some environment variables have the same effects as options passed to python on the command line, as documented in the next section. A few environment variables provide settings not available via command-line options:

PYTHONHOME

The Python installation directory. A lib subdirectory, containing the standard Python library modules, should exist under this directory. On Unix-like systems, the standard library modules should be in subdirectory lib/python-2.3 for Python 2.3, lib/python-2.4 for Python 2.4, and so on.

PYTHONPATH

A list of directories separated by colons on Unix-like systems and by semicolons on Windows. Modules are imported from these directories. This list extends the initial value for Python’s sys.path variable. Modules, importing, and the sys.path variable are covered in Chapter 7 ...

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