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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

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<title>Using matplotlib in a python shell — Matplotlib 1.3.1 documentation</title>

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<h3><a href="../contents.html">Table Of Contents</a></h3>

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<li><a class="reference internal" href="#">Using matplotlib in a python shell</a><ul>

<li><a class="reference internal" href="#ipython-to-the-rescue">Ipython to the rescue</a></li>

<li><a class="reference internal" href="#other-python-interpreters">Other python interpreters</a></li>

<li><a class="reference internal" href="#controlling-interactive-updating">Controlling interactive updating</a></li>

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<span id="mpl-shell"></span><h1>Using matplotlib in a python shell<a class="headerlink" href="#using-matplotlib-in-a-python-shell" title="Permalink to this headline">¶</a></h1>

<p>By default, matplotlib defers drawing until the end of the script

because drawing can be an expensive operation, and you may not want

to update the plot every time a single property is changed, only once

after all the properties have changed.</p>

<p>But when working from the python shell, you usually do want to update

the plot with every command, eg, after changing the

<a class="reference internal" href="../api/pyplot_api.html#matplotlib.pyplot.xlabel" title="matplotlib.pyplot.xlabel"><tt class="xref py py-func docutils literal"><span class="pre">xlabel()</span></tt></a>, or the marker style of a line.

While this is simple in concept, in practice it can be tricky, because

matplotlib is a graphical user interface application under the hood,

and there are some tricks to make the applications work right in a

python shell.</p>

<span id="ipython-pylab"></span><h2>Ipython to the rescue<a class="headerlink" href="#ipython-to-the-rescue" title="Permalink to this headline">¶</a></h2>

<p>Fortunately, <a class="reference external" href="http://ipython.org/">ipython</a>, an enhanced

interactive python shell, has figured out all of these tricks, and is

matplotlib aware, so when you start ipython in the <em>pylab</em> mode.</p>

<div class="highlight-ipython"><div class="highlight"><pre><span class="go">johnh@flag:~> ipython -pylab</span>

<span class="go">Python 2.4.5 (#4, Apr 12 2008, 09:09:16)</span>

<span class="go">IPython 0.9.0 -- An enhanced Interactive Python.</span>

<span class="go"> Welcome to pylab, a matplotlib-based Python environment.</span>

<span class="go"> For more information, type 'help(pylab)'.</span>

<span class="gp">In [1]: </span><span class="n">x</span> <span class="o">=</span> <span class="n">randn</span><span class="p">(</span><span class="mi">10000</span><span class="p">)</span>

</pre></div>

</div>

<p>it sets everything up for you so interactive plotting works as you

would expect it to. Call <a class="reference internal" href="../api/pyplot_api.html#matplotlib.pyplot.figure" title="matplotlib.pyplot.figure"><tt class="xref py py-func docutils literal"><span class="pre">figure()</span></tt></a> and a

figure window pops up, call <a class="reference internal" href="../api/pyplot_api.html#matplotlib.pyplot.plot" title="matplotlib.pyplot.plot"><tt class="xref py py-func docutils literal"><span class="pre">plot()</span></tt></a> and your

data appears in the figure window.</p>

<p>Note in the example above that we did not import any matplotlib names

because in pylab mode, ipython will import them automatically.

ipython also turns on <em>interactive</em> mode for you, which causes every

pyplot command to trigger a figure update, and also provides a

matplotlib aware <tt class="docutils literal"><span class="pre">run</span></tt> command to run matplotlib scripts

efficiently. ipython will turn off interactive mode during a <tt class="docutils literal"><span class="pre">run</span></tt>

command, and then restore the interactive state at the end of the

run so you can continue tweaking the figure manually.</p>

<p>There has been a lot of recent work to embed ipython, with pylab

support, into various GUI applications, so check on the ipython

mailing <a class="reference external" href="http://projects.scipy.org/mailman/listinfo/ipython-user">list</a> for the

latest status.</p>

</div>

<span id="other-shells"></span><h2>Other python interpreters<a class="headerlink" href="#other-python-interpreters" title="Permalink to this headline">¶</a></h2>

<p>If you can’t use ipython, and still want to use matplotlib/pylab from

an interactive python shell, e.g., the plain-ole standard python

interactive interpreter, you

are going to need to understand what a matplotlib backend is

<a class="reference internal" href="../faq/usage_faq.html#what-is-a-backend"><em>What is a backend?</em></a>.</p>

<p>With the TkAgg backend, which uses the Tkinter user interface toolkit,

you can use matplotlib from an arbitrary non-gui python shell. Just set your

<tt class="docutils literal"><span class="pre">backend</span> <span class="pre">:</span> <span class="pre">TkAgg</span></tt> and <tt class="docutils literal"><span class="pre">interactive</span> <span class="pre">:</span> <span class="pre">True</span></tt> in your

<tt class="file docutils literal"><span class="pre">matplotlibrc</span></tt> file (see <a class="reference internal" href="customizing.html#customizing-matplotlib"><em>Customizing matplotlib</em></a>) and fire

up python. Then:</p>

<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">pylab</span> <span class="kn">import</span> <span class="o">*</span>

<span class="gp">>>> </span><span class="n">xlabel</span><span class="p">(</span><span class="s">'hi mom'</span><span class="p">)</span>

</pre></div>

</div>

<p>should work out of the box. This is also likely to work with recent

versions of the qt4agg and gtkagg backends, and with the macosx backend

on the Macintosh. Note, in batch mode,

i.e. when making

figures from scripts, interactive mode can be slow since it redraws

the figure with each command. So you may want to think carefully

before making this the default behavior via the <tt class="file docutils literal"><span class="pre">matplotlibrc</span></tt>

file instead of using the functions listed in the next section.</p>

<p>Gui shells are at best problematic, because they have to run a

mainloop, but interactive plotting also involves a mainloop. Ipython

has sorted all this out for the primary matplotlib backends. There

may be other shells and IDEs that also work with matplotlib in interactive

mode, but one obvious candidate does not:

the python IDLE IDE is a Tkinter gui app that does

not support pylab interactive mode, regardless of backend.</p>

</div>

<span id="controlling-interactive"></span><h2>Controlling interactive updating<a class="headerlink" href="#controlling-interactive-updating" title="Permalink to this headline">¶</a></h2>

<p>The <em>interactive</em> property of the pyplot interface controls whether a

figure canvas is drawn on every pyplot command. If <em>interactive</em> is

<em>False</em>, then the figure state is updated on every plot command, but

will only be drawn on explicit calls to

<a class="reference internal" href="../api/pyplot_api.html#matplotlib.pyplot.draw" title="matplotlib.pyplot.draw"><tt class="xref py py-func docutils literal"><span class="pre">draw()</span></tt></a>. When <em>interactive</em> is

<em>True</em>, then every pyplot command triggers a draw.</p>

<p>The pyplot interface provides 4 commands that are useful for

interactive control.</p>

<dt><a class="reference internal" href="../api/pyplot_api.html#matplotlib.pyplot.isinteractive" title="matplotlib.pyplot.isinteractive"><tt class="xref py py-func docutils literal"><span class="pre">isinteractive()</span></tt></a></dt>

<dd>returns the interactive setting <em>True|False</em></dd>

<dd>turns interactive mode on</dd>

<dd>turns interactive mode off</dd>

<dd>forces a figure redraw</dd>

</dl>

<p>When working with a big figure in which drawing is expensive, you may

want to turn matplotlib’s interactive setting off temporarily to avoid

the performance hit:</p>

<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="c">#create big-expensive-figure</span>

<span class="gp">>>> </span><span class="n">ioff</span><span class="p">()</span> <span class="c"># turn updates off</span>

<span class="gp">>>> </span><span class="n">title</span><span class="p">(</span><span class="s">'now how much would you pay?'</span><span class="p">)</span>

<span class="gp">>>> </span><span class="n">xticklabels</span><span class="p">(</span><span class="n">fontsize</span><span class="o">=</span><span class="mi">20</span><span class="p">,</span> <span class="n">color</span><span class="o">=</span><span class="s">'green'</span><span class="p">)</span>

<span class="gp">>>> </span><span class="n">draw</span><span class="p">()</span> <span class="c"># force a draw</span>

<span class="gp">>>> </span><span class="n">savefig</span><span class="p">(</span><span class="s">'alldone'</span><span class="p">,</span> <span class="n">dpi</span><span class="o">=</span><span class="mi">300</span><span class="p">)</span>

<span class="gp">>>> </span><span class="n">close</span><span class="p">()</span>

<span class="gp">>>> </span><span class="n">ion</span><span class="p">()</span> <span class="c"># turn updating back on</span>

</pre></div>

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