The linecache module allows one to get any line from any file, while attempting to optimize internally, using a cache, the common case where many lines are read from a single file. This is used by the traceback module to retrieve source lines for inclusion in the formatted traceback.
See also
Latest version of the linecache module Python source code
The linecache module defines the following functions:
Get line lineno from file named filename. This function will never raise an exception — it will return '' on errors (the terminating newline character will be included for lines that are found).
If a file named filename is not found, the function will look for it in the module search path, sys.path, after first checking for a PEP 302 __loader__ in module_globals, in case the module was imported from a zipfile or other non-filesystem import source.
New in version 2.5: The module_globals parameter was added.
Example:
>>> import linecache
>>> linecache.getline('/etc/passwd', 4)
'sys:x:3:3:sys:/dev:/bin/sh\n'