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(python2.1-tut.info)Standard Modules

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Standard Modules
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Python comes with a library of standard modules, described in a separate
document, the ("Library Reference" hereafter).  Some modules are built
into the interpreter; these provide access to operations that are not
part of the core of the language but are nevertheless built in, either
for efficiency or to provide access to operating system primitives such
as system calls. The set of such modules is a configuration option;
e.g., the `amoeba' module is only provided on systems that somehow
support Amoeba primitives.  One particular module deserves some
attention: `sys' , which is built into every Python interpreter.  The
variables `sys.ps1' and `sys.ps2' define the strings used as primary
and secondary prompts:

     >>> import sys
     >>> sys.ps1
     '>>> '
     >>> sys.ps2
     '... '
     >>> sys.ps1 = 'C> '
     C> print 'Yuck!'
     Yuck!
     C>

These two variables are only defined if the interpreter is in
interactive mode.

The variable `sys.path' is a list of strings that determine the
interpreter's search path for modules. It is initialized to a default
path taken from the environment variable `PYTHONPATH', or from a
built-in default if `PYTHONPATH' is not set.  You can modify it using
standard list operations, e.g.:

     >>> import sys
     >>> sys.path.append('/ufs/guido/lib/python')