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<div class="section" id="module-StringIO">
<h1>8.5. <tt class="xref docutils literal"><span class="pre">StringIO</span></tt> — Read and write strings as files<a class="headerlink" href="#module-StringIO" title="Permalink to this headline">¶</a></h1>
<p>This module implements a file-like class, <a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO</span></tt></a>, that reads and
writes a string buffer (also known as <em>memory files</em>). See the description of
file objects for operations (section <a class="reference external" href="stdtypes.html#bltin-file-objects"><em>File Objects</em></a>). (For
standard strings, see <a title="str" class="reference external" href="functions.html#str"><tt class="xref docutils literal"><span class="pre">str</span></tt></a> and <a title="unicode" class="reference external" href="functions.html#unicode"><tt class="xref docutils literal"><span class="pre">unicode</span></tt></a>.)</p>
<dl class="class">
<dt id="StringIO.StringIO">
<em class="property">class </em><tt class="descclassname">StringIO.</tt><tt class="descname">StringIO</tt><big>(</big><span class="optional">[</span><em>buffer</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#StringIO.StringIO" title="Permalink to this definition">¶</a></dt>
<dd><p>When a <a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO</span></tt></a> object is created, it can be initialized to an existing
string by passing the string to the constructor. If no string is given, the
<a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO</span></tt></a> will start empty. In both cases, the initial file position
starts at zero.</p>
<p>The <a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO</span></tt></a> object can accept either Unicode or 8-bit strings, but
mixing the two may take some care. If both are used, 8-bit strings that cannot
be interpreted as 7-bit ASCII (that use the 8th bit) will cause a
<a title="exceptions.UnicodeError" class="reference external" href="exceptions.html#exceptions.UnicodeError"><tt class="xref docutils literal"><span class="pre">UnicodeError</span></tt></a> to be raised when <a title="StringIO.StringIO.getvalue" class="reference internal" href="#StringIO.StringIO.getvalue"><tt class="xref docutils literal"><span class="pre">getvalue()</span></tt></a> is called.</p>
</dd></dl>
<p>The following methods of <a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO</span></tt></a> objects require special mention:</p>
<dl class="method">
<dt id="StringIO.StringIO.getvalue">
<tt class="descclassname">StringIO.</tt><tt class="descname">getvalue</tt><big>(</big><big>)</big><a class="headerlink" href="#StringIO.StringIO.getvalue" title="Permalink to this definition">¶</a></dt>
<dd>Retrieve the entire contents of the “file” at any time before the
<a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO</span></tt></a> object’s <a title="StringIO.StringIO.close" class="reference internal" href="#StringIO.StringIO.close"><tt class="xref docutils literal"><span class="pre">close()</span></tt></a> method is called. See the note above
for information about mixing Unicode and 8-bit strings; such mixing can cause
this method to raise <a title="exceptions.UnicodeError" class="reference external" href="exceptions.html#exceptions.UnicodeError"><tt class="xref docutils literal"><span class="pre">UnicodeError</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="StringIO.StringIO.close">
<tt class="descclassname">StringIO.</tt><tt class="descname">close</tt><big>(</big><big>)</big><a class="headerlink" href="#StringIO.StringIO.close" title="Permalink to this definition">¶</a></dt>
<dd>Free the memory buffer. Attempting to do further operations with a closed
<a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO</span></tt></a> object will raise a <a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref docutils literal"><span class="pre">ValueError</span></tt></a>.</dd></dl>
<p>Example usage:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">StringIO</span>
<span class="n">output</span> <span class="o">=</span> <span class="n">StringIO</span><span class="o">.</span><span class="n">StringIO</span><span class="p">()</span>
<span class="n">output</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">'First line.</span><span class="se">\n</span><span class="s">'</span><span class="p">)</span>
<span class="k">print</span> <span class="o">>></span><span class="n">output</span><span class="p">,</span> <span class="s">'Second line.'</span>
<span class="c"># Retrieve file contents -- this will be</span>
<span class="c"># 'First line.\nSecond line.\n'</span>
<span class="n">contents</span> <span class="o">=</span> <span class="n">output</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span>
<span class="c"># Close object and discard memory buffer --</span>
<span class="c"># .getvalue() will now raise an exception.</span>
<span class="n">output</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</div>
<div class="section" id="module-cStringIO">
<h1>8.6. <tt class="xref docutils literal"><span class="pre">cStringIO</span></tt> — Faster version of <tt class="xref docutils literal"><span class="pre">StringIO</span></tt><a class="headerlink" href="#module-cStringIO" title="Permalink to this headline">¶</a></h1>
<p>The module <tt class="xref docutils literal"><span class="pre">cStringIO</span></tt> provides an interface similar to that of the
<tt class="xref docutils literal"><span class="pre">StringIO</span></tt> module. Heavy use of <a title="StringIO.StringIO" class="reference internal" href="#StringIO.StringIO"><tt class="xref docutils literal"><span class="pre">StringIO.StringIO</span></tt></a> objects can be
made more efficient by using the function <tt class="xref docutils literal"><span class="pre">StringIO()</span></tt> from this module
instead.</p>
<p>Since this module provides a factory function which returns objects of built-in
types, there’s no way to build your own version using subclassing. It’s not
possible to set attributes on it. Use the original <tt class="xref docutils literal"><span class="pre">StringIO</span></tt> module in
those cases.</p>
<p>Unlike the memory files implemented by the <tt class="xref docutils literal"><span class="pre">StringIO</span></tt> module, those
provided by this module are not able to accept Unicode strings that cannot be
encoded as plain ASCII strings.</p>
<p>Calling <tt class="xref docutils literal"><span class="pre">StringIO()</span></tt> with a Unicode string parameter populates
the object with the buffer representation of the Unicode string, instead of
encoding the string.</p>
<p>Another difference from the <tt class="xref docutils literal"><span class="pre">StringIO</span></tt> module is that calling
<tt class="xref docutils literal"><span class="pre">StringIO()</span></tt> with a string parameter creates a read-only object. Unlike an
object created without a string parameter, it does not have write methods.
These objects are not generally visible. They turn up in tracebacks as
<tt class="xref docutils literal"><span class="pre">StringI</span></tt> and <tt class="xref docutils literal"><span class="pre">StringO</span></tt>.</p>
<p>The following data objects are provided as well:</p>
<dl class="data">
<dt id="cStringIO.InputType">
<tt class="descclassname">cStringIO.</tt><tt class="descname">InputType</tt><a class="headerlink" href="#cStringIO.InputType" title="Permalink to this definition">¶</a></dt>
<dd>The type object of the objects created by calling <tt class="xref docutils literal"><span class="pre">StringIO()</span></tt> with a string
parameter.</dd></dl>
<dl class="data">
<dt id="cStringIO.OutputType">
<tt class="descclassname">cStringIO.</tt><tt class="descname">OutputType</tt><a class="headerlink" href="#cStringIO.OutputType" title="Permalink to this definition">¶</a></dt>
<dd>The type object of the objects returned by calling <tt class="xref docutils literal"><span class="pre">StringIO()</span></tt> with no
parameters.</dd></dl>
<p>There is a C API to the module as well; refer to the module source for more
information.</p>
<p>Example usage:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">cStringIO</span>
<span class="n">output</span> <span class="o">=</span> <span class="n">cStringIO</span><span class="o">.</span><span class="n">StringIO</span><span class="p">()</span>
<span class="n">output</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">'First line.</span><span class="se">\n</span><span class="s">'</span><span class="p">)</span>
<span class="k">print</span> <span class="o">>></span><span class="n">output</span><span class="p">,</span> <span class="s">'Second line.'</span>
<span class="c"># Retrieve file contents -- this will be</span>
<span class="c"># 'First line.\nSecond line.\n'</span>
<span class="n">contents</span> <span class="o">=</span> <span class="n">output</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span>
<span class="c"># Close object and discard memory buffer --</span>
<span class="c"># .getvalue() will now raise an exception.</span>
<span class="n">output</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#">8.5. <tt class="docutils literal"><span class="pre">StringIO</span></tt> — Read and write strings as files</a></li>
<li><a class="reference external" href="#module-cStringIO">8.6. <tt class="docutils literal"><span class="pre">cStringIO</span></tt> — Faster version of <tt class="docutils literal"><span class="pre">StringIO</span></tt></a></li>
</ul>
<h4>Previous topic</h4>
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<h4>Next topic</h4>
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