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<section id="troubleshooting">
<h1><span class="section-number">2.10. </span>Troubleshooting<a class="headerlink" href="#troubleshooting" title="Link to this heading"></a></h1>
<section id="testing-if-python-can-launch-lammps">
<h2><span class="section-number">2.10.1. </span>Testing if Python can launch LAMMPS<a class="headerlink" href="#testing-if-python-can-launch-lammps" title="Link to this heading"></a></h2>
<p>To test if LAMMPS is callable from Python, launch Python interactively
and type:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">lammps</span><span class="w"> </span><span class="kn">import</span> <span class="n">lammps</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">lmp</span> <span class="o">=</span> <span class="n">lammps</span><span class="p">()</span>
</pre></div>
</div>
<p>If you get no errors, youre ready to use LAMMPS from Python. If the
second command fails, the most common error to see is</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>OSError:<span class="w"> </span>Could<span class="w"> </span>not<span class="w"> </span>load<span class="w"> </span>LAMMPS<span class="w"> </span>dynamic<span class="w"> </span>library
</pre></div>
</div>
<p>which means Python was unable to load the LAMMPS shared library. This
typically occurs if the system cant find the LAMMPS shared library or
one of the auxiliary shared libraries it depends on, or if something
about the library is incompatible with your Python. The error message
should give you an indication of what went wrong.</p>
<p>If your shared library uses a suffix, such as <code class="docutils literal notranslate"><span class="pre">liblammps_mpi.so</span></code>, change
the constructor call as follows (see <a class="reference internal" href="Python_create.html#python-create-lammps"><span class="std std-ref">Creating or deleting a LAMMPS object</span></a> for more details):</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">lmp</span> <span class="o">=</span> <span class="n">lammps</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">&#39;mpi&#39;</span><span class="p">)</span>
</pre></div>
</div>
<p>You can also test the load directly in Python as follows, without
first importing from the <code class="docutils literal notranslate"><span class="pre">lammps</span></code> module:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span><span class="w"> </span><span class="nn">ctypes</span><span class="w"> </span><span class="kn">import</span> <span class="n">CDLL</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">CDLL</span><span class="p">(</span><span class="s2">&quot;liblammps.so&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>If an error occurs, carefully go through the steps in <a class="reference internal" href="Python_install.html#python-install-guides"><span class="std std-ref">Installing the LAMMPS Python Module and Shared Library</span></a> and on the
<a class="reference internal" href="Build_basics.html"><span class="doc">Build_basics</span></a> page about building a shared library.</p>
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