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<div class="section" id="s-outputting-csv-with-django">
<span id="outputting-csv-with-django"></span><h1>Outputting CSV with Django<a class="headerlink" href="#outputting-csv-with-django" title="Permalink to this headline">¶</a></h1>
<p>This document explains how to output CSV (Comma Separated Values) dynamically
using Django views. To do this, you can either use the Python CSV library or the
Django template system.</p>
<div class="section" id="s-using-the-python-csv-library">
<span id="using-the-python-csv-library"></span><h2>Using the Python CSV library<a class="headerlink" href="#using-the-python-csv-library" title="Permalink to this headline">¶</a></h2>
<p>Python comes with a CSV library, <code class="xref py py-mod docutils literal"><span class="pre">csv</span></code>. The key to using it with Django is
that the <code class="xref py py-mod docutils literal"><span class="pre">csv</span></code> module’s CSV-creation capability acts on file-like objects,
and Django’s <a class="reference internal" href="../ref/request-response.html#django.http.HttpResponse" title="django.http.HttpResponse"><code class="xref py py-class docutils literal"><span class="pre">HttpResponse</span></code></a> objects are file-like objects.</p>
<p>Here’s an example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="kn">from</span> <span class="nn">django.http</span> <span class="k">import</span> <span class="n">HttpResponse</span>
<span class="k">def</span> <span class="nf">some_view</span><span class="p">(</span><span class="n">request</span><span class="p">):</span>
<span class="c1"># Create the HttpResponse object with the appropriate CSV header.</span>
<span class="n">response</span> <span class="o">=</span> <span class="n">HttpResponse</span><span class="p">(</span><span class="n">content_type</span><span class="o">=</span><span class="s1">'text/csv'</span><span class="p">)</span>
<span class="n">response</span><span class="p">[</span><span class="s1">'Content-Disposition'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'attachment; filename="somefilename.csv"'</span>
<span class="n">writer</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">writer</span><span class="p">(</span><span class="n">response</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">([</span><span class="s1">'First row'</span><span class="p">,</span> <span class="s1">'Foo'</span><span class="p">,</span> <span class="s1">'Bar'</span><span class="p">,</span> <span class="s1">'Baz'</span><span class="p">])</span>
<span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">([</span><span class="s1">'Second row'</span><span class="p">,</span> <span class="s1">'A'</span><span class="p">,</span> <span class="s1">'B'</span><span class="p">,</span> <span class="s1">'C'</span><span class="p">,</span> <span class="s1">'"Testing"'</span><span class="p">,</span> <span class="s2">"Here's a quote"</span><span class="p">])</span>
<span class="k">return</span> <span class="n">response</span>
</pre></div>
</div>
<p>The code and comments should be self-explanatory, but a few things deserve a
mention:</p>
<ul class="simple">
<li>The response gets a special MIME type, <em class="mimetype">text/csv</em>. This tells
browsers that the document is a CSV file, rather than an HTML file. If
you leave this off, browsers will probably interpret the output as HTML,
which will result in ugly, scary gobbledygook in the browser window.</li>
<li>The response gets an additional <code class="docutils literal"><span class="pre">Content-Disposition</span></code> header, which
contains the name of the CSV file. This filename is arbitrary; call it
whatever you want. It’ll be used by browsers in the “Save as...” dialog, etc.</li>
<li>Hooking into the CSV-generation API is easy: Just pass <code class="docutils literal"><span class="pre">response</span></code> as the
first argument to <code class="docutils literal"><span class="pre">csv.writer</span></code>. The <code class="docutils literal"><span class="pre">csv.writer</span></code> function expects a
file-like object, and <a class="reference internal" href="../ref/request-response.html#django.http.HttpResponse" title="django.http.HttpResponse"><code class="xref py py-class docutils literal"><span class="pre">HttpResponse</span></code></a> objects fit the
bill.</li>
<li>For each row in your CSV file, call <code class="docutils literal"><span class="pre">writer.writerow</span></code>, passing it an
iterable object such as a list or tuple.</li>
<li>The CSV module takes care of quoting for you, so you don’t have to worry
about escaping strings with quotes or commas in them. Just pass
<code class="docutils literal"><span class="pre">writerow()</span></code> your raw strings, and it’ll do the right thing.</li>
</ul>
<div class="admonition-handling-unicode-on-python-2 admonition">
<p class="first admonition-title">Handling Unicode on Python 2</p>
<p>Python 2’s <code class="xref py py-mod docutils literal"><span class="pre">csv</span></code> module does not support Unicode input. Since Django
uses Unicode internally this means strings read from sources such as
<a class="reference internal" href="../ref/request-response.html#django.http.HttpRequest" title="django.http.HttpRequest"><code class="xref py py-class docutils literal"><span class="pre">HttpRequest</span></code></a> are potentially problematic. There are a
few options for handling this:</p>
<ul class="simple">
<li>Manually encode all Unicode objects to a compatible encoding.</li>
<li>Use the <code class="docutils literal"><span class="pre">UnicodeWriter</span></code> class provided in the <a class="reference external" href="https://docs.python.org/library/csv.html#examples">csv module’s examples
section</a>.</li>
<li>Use the <a class="reference external" href="https://github.com/jdunck/python-unicodecsv">python-unicodecsv module</a>, which aims to be a drop-in
replacement for <code class="xref py py-mod docutils literal"><span class="pre">csv</span></code> that gracefully handles Unicode.</li>
</ul>
<p class="last">For more information, see the Python documentation of the <code class="xref py py-mod docutils literal"><span class="pre">csv</span></code> module.</p>
</div>
<div class="section" id="s-streaming-large-csv-files">
<span id="s-streaming-csv-files"></span><span id="streaming-large-csv-files"></span><span id="streaming-csv-files"></span><h3>Streaming large CSV files<a class="headerlink" href="#streaming-large-csv-files" title="Permalink to this headline">¶</a></h3>
<p>When dealing with views that generate very large responses, you might want to
consider using Django’s <a class="reference internal" href="../ref/request-response.html#django.http.StreamingHttpResponse" title="django.http.StreamingHttpResponse"><code class="xref py py-class docutils literal"><span class="pre">StreamingHttpResponse</span></code></a> instead.
For example, by streaming a file that takes a long time to generate you can
avoid a load balancer dropping a connection that might have otherwise timed out
while the server was generating the response.</p>
<p>In this example, we make full use of Python generators to efficiently handle
the assembly and transmission of a large CSV file:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="kn">from</span> <span class="nn">django.utils.six.moves</span> <span class="k">import</span> <span class="nb">range</span>
<span class="kn">from</span> <span class="nn">django.http</span> <span class="k">import</span> <span class="n">StreamingHttpResponse</span>
<span class="k">class</span> <span class="nc">Echo</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="sd">"""An object that implements just the write method of the file-like</span>
<span class="sd"> interface.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">write</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span>
<span class="sd">"""Write the value by returning it, instead of storing in a buffer."""</span>
<span class="k">return</span> <span class="n">value</span>
<span class="k">def</span> <span class="nf">some_streaming_csv_view</span><span class="p">(</span><span class="n">request</span><span class="p">):</span>
<span class="sd">"""A view that streams a large CSV file."""</span>
<span class="c1"># Generate a sequence of rows. The range is based on the maximum number of</span>
<span class="c1"># rows that can be handled by a single sheet in most spreadsheet</span>
<span class="c1"># applications.</span>
<span class="n">rows</span> <span class="o">=</span> <span class="p">([</span><span class="s2">"Row </span><span class="si">{}</span><span class="s2">"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">idx</span><span class="p">),</span> <span class="nb">str</span><span class="p">(</span><span class="n">idx</span><span class="p">)]</span> <span class="k">for</span> <span class="n">idx</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">65536</span><span class="p">))</span>
<span class="n">pseudo_buffer</span> <span class="o">=</span> <span class="n">Echo</span><span class="p">()</span>
<span class="n">writer</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">writer</span><span class="p">(</span><span class="n">pseudo_buffer</span><span class="p">)</span>
<span class="n">response</span> <span class="o">=</span> <span class="n">StreamingHttpResponse</span><span class="p">((</span><span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">(</span><span class="n">row</span><span class="p">)</span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">rows</span><span class="p">),</span>
<span class="n">content_type</span><span class="o">=</span><span class="s2">"text/csv"</span><span class="p">)</span>
<span class="n">response</span><span class="p">[</span><span class="s1">'Content-Disposition'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'attachment; filename="somefilename.csv"'</span>
<span class="k">return</span> <span class="n">response</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="s-using-the-template-system">
<span id="using-the-template-system"></span><h2>Using the template system<a class="headerlink" href="#using-the-template-system" title="Permalink to this headline">¶</a></h2>
<p>Alternatively, you can use the <a class="reference internal" href="../topics/templates.html"><span class="doc">Django template system</span></a>
to generate CSV. This is lower-level than using the convenient Python <code class="xref py py-mod docutils literal"><span class="pre">csv</span></code>
module, but the solution is presented here for completeness.</p>
<p>The idea here is to pass a list of items to your template, and have the
template output the commas in a <a class="reference internal" href="../ref/templates/builtins.html#std:templatetag-for"><code class="xref std std-ttag docutils literal"><span class="pre">for</span></code></a> loop.</p>
<p>Here’s an example, which generates the same CSV file as above:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">django.http</span> <span class="k">import</span> <span class="n">HttpResponse</span>
<span class="kn">from</span> <span class="nn">django.template</span> <span class="k">import</span> <span class="n">loader</span><span class="p">,</span> <span class="n">Context</span>
<span class="k">def</span> <span class="nf">some_view</span><span class="p">(</span><span class="n">request</span><span class="p">):</span>
<span class="c1"># Create the HttpResponse object with the appropriate CSV header.</span>
<span class="n">response</span> <span class="o">=</span> <span class="n">HttpResponse</span><span class="p">(</span><span class="n">content_type</span><span class="o">=</span><span class="s1">'text/csv'</span><span class="p">)</span>
<span class="n">response</span><span class="p">[</span><span class="s1">'Content-Disposition'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'attachment; filename="somefilename.csv"'</span>
<span class="c1"># The data is hard-coded here, but you could load it from a database or</span>
<span class="c1"># some other source.</span>
<span class="n">csv_data</span> <span class="o">=</span> <span class="p">(</span>
<span class="p">(</span><span class="s1">'First row'</span><span class="p">,</span> <span class="s1">'Foo'</span><span class="p">,</span> <span class="s1">'Bar'</span><span class="p">,</span> <span class="s1">'Baz'</span><span class="p">),</span>
<span class="p">(</span><span class="s1">'Second row'</span><span class="p">,</span> <span class="s1">'A'</span><span class="p">,</span> <span class="s1">'B'</span><span class="p">,</span> <span class="s1">'C'</span><span class="p">,</span> <span class="s1">'"Testing"'</span><span class="p">,</span> <span class="s2">"Here's a quote"</span><span class="p">),</span>
<span class="p">)</span>
<span class="n">t</span> <span class="o">=</span> <span class="n">loader</span><span class="o">.</span><span class="n">get_template</span><span class="p">(</span><span class="s1">'my_template_name.txt'</span><span class="p">)</span>
<span class="n">c</span> <span class="o">=</span> <span class="n">Context</span><span class="p">({</span>
<span class="s1">'data'</span><span class="p">:</span> <span class="n">csv_data</span><span class="p">,</span>
<span class="p">})</span>
<span class="n">response</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">t</span><span class="o">.</span><span class="n">render</span><span class="p">(</span><span class="n">c</span><span class="p">))</span>
<span class="k">return</span> <span class="n">response</span>
</pre></div>
</div>
<p>The only difference between this example and the previous example is that this
one uses template loading instead of the CSV module. The rest of the code –
such as the <code class="docutils literal"><span class="pre">content_type='text/csv'</span></code> – is the same.</p>
<p>Then, create the template <code class="docutils literal"><span class="pre">my_template_name.txt</span></code>, with this template code:</p>
<div class="highlight-html+django"><div class="highlight"><pre><span></span><span class="cp">{%</span> <span class="k">for</span> <span class="nv">row</span> <span class="k">in</span> <span class="nv">data</span> <span class="cp">%}</span>"<span class="cp">{{</span> <span class="nv">row.0</span><span class="o">|</span><span class="nf">addslashes</span> <span class="cp">}}</span>", "<span class="cp">{{</span> <span class="nv">row.1</span><span class="o">|</span><span class="nf">addslashes</span> <span class="cp">}}</span>", "<span class="cp">{{</span> <span class="nv">row.2</span><span class="o">|</span><span class="nf">addslashes</span> <span class="cp">}}</span>", "<span class="cp">{{</span> <span class="nv">row.3</span><span class="o">|</span><span class="nf">addslashes</span> <span class="cp">}}</span>", "<span class="cp">{{</span> <span class="nv">row.4</span><span class="o">|</span><span class="nf">addslashes</span> <span class="cp">}}</span>"
<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
</pre></div>
</div>
<p>This template is quite basic. It just iterates over the given data and displays
a line of CSV for each row. It uses the <a class="reference internal" href="../ref/templates/builtins.html#std:templatefilter-addslashes"><code class="xref std std-tfilter docutils literal"><span class="pre">addslashes</span></code></a> template filter to
ensure there aren’t any problems with quotes.</p>
</div>
<div class="section" id="s-other-text-based-formats">
<span id="other-text-based-formats"></span><h2>Other text-based formats<a class="headerlink" href="#other-text-based-formats" title="Permalink to this headline">¶</a></h2>
<p>Notice that there isn’t very much specific to CSV here – just the specific
output format. You can use either of these techniques to output any text-based
format you can dream of. You can also use a similar technique to generate
arbitrary binary data; see <a class="reference internal" href="outputting-pdf.html"><span class="doc">Outputting PDFs with Django</span></a> for an example.</p>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Outputting CSV with Django</a><ul>
<li><a class="reference internal" href="#using-the-python-csv-library">Using the Python CSV library</a><ul>
<li><a class="reference internal" href="#streaming-large-csv-files">Streaming large CSV files</a></li>
</ul>
</li>
<li><a class="reference internal" href="#using-the-template-system">Using the template system</a></li>
<li><a class="reference internal" href="#other-text-based-formats">Other text-based formats</a></li>
</ul>
</li>
</ul>
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