Python comes with a library of standard modules, described in a separate
document (Python Library Reference). 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') >>>