1:mod:`linecache` --- Random access to text lines 2================================================ 3 4.. module:: linecache 5 :synopsis: Provides random access to individual lines from text files. 6 7.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il> 8 9**Source code:** :source:`Lib/linecache.py` 10 11-------------- 12 13The :mod:`linecache` module allows one to get any line from a Python source file, while 14attempting to optimize internally, using a cache, the common case where many 15lines are read from a single file. This is used by the :mod:`traceback` module 16to retrieve source lines for inclusion in the formatted traceback. 17 18The :func:`tokenize.open` function is used to open files. This 19function uses :func:`tokenize.detect_encoding` to get the encoding of the 20file; in the absence of an encoding token, the file encoding defaults to UTF-8. 21 22The :mod:`linecache` module defines the following functions: 23 24 25.. function:: getline(filename, lineno, module_globals=None) 26 27 Get line *lineno* from file named *filename*. This function will never raise an 28 exception --- it will return ``''`` on errors (the terminating newline character 29 will be included for lines that are found). 30 31 .. index:: triple: module; search; path 32 33 If a file named *filename* is not found, the function first checks 34 for a :pep:`302` ``__loader__`` in *module_globals*. 35 If there is such a loader and it defines a ``get_source`` method, 36 then that determines the source lines 37 (if ``get_source()`` returns ``None``, then ``''`` is returned). 38 Finally, if *filename* is a relative filename, 39 it is looked up relative to the entries in the module search path, ``sys.path``. 40 41 42.. function:: clearcache() 43 44 Clear the cache. Use this function if you no longer need lines from files 45 previously read using :func:`getline`. 46 47 48.. function:: checkcache(filename=None) 49 50 Check the cache for validity. Use this function if files in the cache may have 51 changed on disk, and you require the updated version. If *filename* is omitted, 52 it will check all the entries in the cache. 53 54.. function:: lazycache(filename, module_globals) 55 56 Capture enough detail about a non-file-based module to permit getting its 57 lines later via :func:`getline` even if *module_globals* is ``None`` in the later 58 call. This avoids doing I/O until a line is actually needed, without having 59 to carry the module globals around indefinitely. 60 61 .. versionadded:: 3.5 62 63Example:: 64 65 >>> import linecache 66 >>> linecache.getline(linecache.__file__, 8) 67 'import sys\n' 68