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<section id="module-linecache">
<span id="linecache-random-access-to-text-lines"></span><h1><a class="reference internal" href="#module-linecache" title="linecache: Provides random access to individual lines from text files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">linecache</span></code></a> — Random access to text lines<a class="headerlink" href="#module-linecache" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.10/Lib/linecache.py">Lib/linecache.py</a></p>
<hr class="docutils" />
<p>The <a class="reference internal" href="#module-linecache" title="linecache: Provides random access to individual lines from text files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">linecache</span></code></a> 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 <a class="reference internal" href="traceback.html#module-traceback" title="traceback: Print or retrieve a stack traceback."><code class="xref py py-mod docutils literal notranslate"><span class="pre">traceback</span></code></a> module
to retrieve source lines for inclusion in the formatted traceback.</p>
<p>The <a class="reference internal" href="tokenize.html#tokenize.open" title="tokenize.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">tokenize.open()</span></code></a> function is used to open files. This
function uses <a class="reference internal" href="tokenize.html#tokenize.detect_encoding" title="tokenize.detect_encoding"><code class="xref py py-func docutils literal notranslate"><span class="pre">tokenize.detect_encoding()</span></code></a> to get the encoding of the
file; in the absence of an encoding token, the file encoding defaults to UTF-8.</p>
<p>The <a class="reference internal" href="#module-linecache" title="linecache: Provides random access to individual lines from text files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">linecache</span></code></a> module defines the following functions:</p>
<dl class="py function">
<dt class="sig sig-object py" id="linecache.getline">
<span class="sig-prename descclassname"><span class="pre">linecache.</span></span><span class="sig-name descname"><span class="pre">getline</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">filename</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">lineno</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">module_globals</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#linecache.getline" title="Permalink to this definition">¶</a></dt>
<dd><p>Get line <em>lineno</em> from file named <em>filename</em>. This function will never raise an
exception — it will return <code class="docutils literal notranslate"><span class="pre">''</span></code> on errors (the terminating newline character
will be included for lines that are found).</p>
<p id="index-0">If a file named <em>filename</em> is not found, the function first checks
for a <span class="target" id="index-1"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> <code class="docutils literal notranslate"><span class="pre">__loader__</span></code> in <em>module_globals</em>.
If there is such a loader and it defines a <code class="docutils literal notranslate"><span class="pre">get_source</span></code> method,
then that determines the source lines
(if <code class="docutils literal notranslate"><span class="pre">get_source()</span></code> returns <code class="docutils literal notranslate"><span class="pre">None</span></code>, then <code class="docutils literal notranslate"><span class="pre">''</span></code> is returned).
Finally, if <em>filename</em> is a relative filename,
it is looked up relative to the entries in the module search path, <code class="docutils literal notranslate"><span class="pre">sys.path</span></code>.</p>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="linecache.clearcache">
<span class="sig-prename descclassname"><span class="pre">linecache.</span></span><span class="sig-name descname"><span class="pre">clearcache</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#linecache.clearcache" title="Permalink to this definition">¶</a></dt>
<dd><p>Clear the cache. Use this function if you no longer need lines from files
previously read using <a class="reference internal" href="#linecache.getline" title="linecache.getline"><code class="xref py py-func docutils literal notranslate"><span class="pre">getline()</span></code></a>.</p>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="linecache.checkcache">
<span class="sig-prename descclassname"><span class="pre">linecache.</span></span><span class="sig-name descname"><span class="pre">checkcache</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">filename</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#linecache.checkcache" title="Permalink to this definition">¶</a></dt>
<dd><p>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 <em>filename</em> is omitted,
it will check all the entries in the cache.</p>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="linecache.lazycache">
<span class="sig-prename descclassname"><span class="pre">linecache.</span></span><span class="sig-name descname"><span class="pre">lazycache</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">filename</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">module_globals</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#linecache.lazycache" title="Permalink to this definition">¶</a></dt>
<dd><p>Capture enough detail about a non-file-based module to permit getting its
lines later via <a class="reference internal" href="#linecache.getline" title="linecache.getline"><code class="xref py py-func docutils literal notranslate"><span class="pre">getline()</span></code></a> even if <em>module_globals</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> in the later
call. This avoids doing I/O until a line is actually needed, without having
to carry the module globals around indefinitely.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
</dd></dl>
<p>Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">linecache</span>
<span class="gp">>>> </span><span class="n">linecache</span><span class="o">.</span><span class="n">getline</span><span class="p">(</span><span class="n">linecache</span><span class="o">.</span><span class="vm">__file__</span><span class="p">,</span> <span class="mi">8</span><span class="p">)</span>
<span class="go">'import sys\n'</span>
</pre></div>
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