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:mod:`linecache` --- Random access to text lines
================================================
.. module:: linecache
:synopsis: Provides random access to individual lines from text files.
.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
**Source code:** :source:`Lib/linecache.py`
--------------
The :mod:`linecache` module allows one to get any line from a Python source 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 :mod:`traceback` module
to retrieve source lines for inclusion in the formatted traceback.
The :func:`tokenize.open` function is used to open files. This
function uses :func:`tokenize.detect_encoding` to get the encoding of the
file; in the absence of an encoding token, the file encoding defaults to UTF-8.
The :mod:`linecache` module defines the following functions:
.. function:: getline(filename, lineno, module_globals=None)
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).
.. index:: triple: module; search; path
If a file named *filename* is not found, the function first checks
for a :pep:`302` ``__loader__`` in *module_globals*.
If there is such a loader and it defines a ``get_source`` method,
then that determines the source lines
(if ``get_source()`` returns ``None``, then ``''`` is returned).
Finally, if *filename* is a relative filename,
it is looked up relative to the entries in the module search path, ``sys.path``.
.. function:: clearcache()
Clear the cache. Use this function if you no longer need lines from files
previously read using :func:`getline`.
.. function:: checkcache(filename=None)
Check the cache for validity. Use this function if files in the cache may have
changed on disk, and you require the updated version. If *filename* is omitted,
it will check all the entries in the cache.
.. function:: lazycache(filename, module_globals)
Capture enough detail about a non-file-based module to permit getting its
lines later via :func:`getline` even if *module_globals* is ``None`` in the later
call. This avoids doing I/O until a line is actually needed, without having
to carry the module globals around indefinitely.
.. versionadded:: 3.5
Example::
>>> import linecache
>>> linecache.getline(linecache.__file__, 8)
'import sys\n'
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