Major Built-in Modules

Built-in modules are always available, but must be imported to be used in clients. Either use “import module” and qualify names (“”), or “from module import...” and use names unqualified (“name”). There are dozens of built-in modules; the next sections document the most commonly used.

The sys Module

Contains interpreter-specific exports.


Command-line argument strings list: [command, arguments . . . ]. Like C’s “argv” array.


List of names of C modules compiled into this Python.

exc_info( )

Returns tuple of three values describing the exception currently being handled: (type, value, traceback). Specific to current thread. Subsumes exc_type, exc_value, and exc_traceback in Python 1.5 and later.


Type of exception being handled (when an exception has been raised). Not thread-specific.


Exception’s parameter (second argument to raise). Not thread-specific.


Exception’s traceback object. Not thread-specific.


Assign a string giving the site-specific directory prefix where the platform-dependent Python files are installed; defaults to “/usr/local,” or a build-time argument. Used to locate shared library modules (in <exec_ prefix>/lib/python<version >/lib-dynload ), and configuration files.


File pathname of Python interperter.


Exits from python process with status N, by raising SystemExit (can be caught in a try and ignored).


Assign a no-argument function to be called on exits.

getrefcount(object) ...

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