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<li><a class="reference internal" href="#">1. Embedding Python in Another Application</a><ul>
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<li><a class="reference internal" href="#very-high-level-embedding">1.1. Very High Level Embedding</a></li>
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<li><a class="reference internal" href="#beyond-very-high-level-embedding-an-overview">1.2. Beyond Very High Level Embedding: An overview</a></li>
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<li><a class="reference internal" href="#pure-embedding">1.3. Pure Embedding</a></li>
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<li><a class="reference internal" href="#extending-embedded-python">1.4. Extending Embedded Python</a></li>
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<li><a class="reference internal" href="#embedding-python-in-c">1.5. Embedding Python in C++</a></li>
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<li><a class="reference internal" href="#compiling-and-linking-under-unix-like-systems">1.6. Compiling and Linking under Unix-like systems</a></li>
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<section id="embedding-python-in-another-application">
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<span id="embedding"></span><h1><span class="section-number">1. </span>Embedding Python in Another Application<a class="headerlink" href="#embedding-python-in-another-application" title="Link to this heading">¶</a></h1>
|
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<p>The previous chapters discussed how to extend Python, that is, how to extend the
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functionality of Python by attaching a library of C functions to it. It is also
|
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possible to do it the other way around: enrich your C/C++ application by
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embedding Python in it. Embedding provides your application with the ability to
|
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implement some of the functionality of your application in Python rather than C
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or C++. This can be used for many purposes; one example would be to allow users
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to tailor the application to their needs by writing some scripts in Python. You
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can also use it yourself if some of the functionality can be written in Python
|
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more easily.</p>
|
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<p>Embedding Python is similar to extending it, but not quite. The difference is
|
||
that when you extend Python, the main program of the application is still the
|
||
Python interpreter, while if you embed Python, the main program may have nothing
|
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to do with Python — instead, some parts of the application occasionally call
|
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the Python interpreter to run some Python code.</p>
|
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<p>So if you are embedding Python, you are providing your own main program. One of
|
||
the things this main program has to do is initialize the Python interpreter. At
|
||
the very least, you have to call the function <a class="reference internal" href="../c-api/init.html#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>. There are
|
||
optional calls to pass command line arguments to Python. Then later you can
|
||
call the interpreter from any part of the application.</p>
|
||
<p>There are several different ways to call the interpreter: you can pass a string
|
||
containing Python statements to <a class="reference internal" href="../c-api/veryhigh.html#c.PyRun_SimpleString" title="PyRun_SimpleString"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyRun_SimpleString()</span></code></a>, or you can pass a
|
||
stdio file pointer and a file name (for identification in error messages only)
|
||
to <a class="reference internal" href="../c-api/veryhigh.html#c.PyRun_SimpleFile" title="PyRun_SimpleFile"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyRun_SimpleFile()</span></code></a>. You can also call the lower-level operations
|
||
described in the previous chapters to construct and use Python objects.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><a class="reference internal" href="../c-api/index.html#c-api-index"><span class="std std-ref">Python/C API Reference Manual</span></a></dt><dd><p>The details of Python’s C interface are given in this manual. A great deal of
|
||
necessary information can be found here.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
<section id="very-high-level-embedding">
|
||
<span id="high-level-embedding"></span><h2><span class="section-number">1.1. </span>Very High Level Embedding<a class="headerlink" href="#very-high-level-embedding" title="Link to this heading">¶</a></h2>
|
||
<p>The simplest form of embedding Python is the use of the very high level
|
||
interface. This interface is intended to execute a Python script without needing
|
||
to interact with the application directly. This can for example be used to
|
||
perform some operation on a file.</p>
|
||
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define PY_SSIZE_T_CLEAN</span>
|
||
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><Python.h></span>
|
||
|
||
<span class="kt">int</span>
|
||
<span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">argv</span><span class="p">[])</span>
|
||
<span class="p">{</span>
|
||
<span class="w"> </span><span class="n">PyStatus</span><span class="w"> </span><span class="n">status</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="n">PyConfig</span><span class="w"> </span><span class="n">config</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="n">PyConfig_InitPythonConfig</span><span class="p">(</span><span class="o">&</span><span class="n">config</span><span class="p">);</span>
|
||
|
||
<span class="w"> </span><span class="cm">/* optional but recommended */</span>
|
||
<span class="w"> </span><span class="n">status</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyConfig_SetBytesString</span><span class="p">(</span><span class="o">&</span><span class="n">config</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">config</span><span class="p">.</span><span class="n">program_name</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">0</span><span class="p">]);</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">PyStatus_Exception</span><span class="p">(</span><span class="n">status</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="k">goto</span><span class="w"> </span><span class="n">exception</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
|
||
<span class="w"> </span><span class="n">status</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Py_InitializeFromConfig</span><span class="p">(</span><span class="o">&</span><span class="n">config</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">PyStatus_Exception</span><span class="p">(</span><span class="n">status</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="k">goto</span><span class="w"> </span><span class="n">exception</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="n">PyConfig_Clear</span><span class="p">(</span><span class="o">&</span><span class="n">config</span><span class="p">);</span>
|
||
|
||
<span class="w"> </span><span class="n">PyRun_SimpleString</span><span class="p">(</span><span class="s">"from time import time,ctime</span><span class="se">\n</span><span class="s">"</span>
|
||
<span class="w"> </span><span class="s">"print('Today is', ctime(time()))</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">Py_FinalizeEx</span><span class="p">()</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">exit</span><span class="p">(</span><span class="mi">120</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
|
||
|
||
<span class="w"> </span><span class="nl">exception</span><span class="p">:</span>
|
||
<span class="w"> </span><span class="n">PyConfig_Clear</span><span class="p">(</span><span class="o">&</span><span class="n">config</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">Py_ExitStatusException</span><span class="p">(</span><span class="n">status</span><span class="p">);</span>
|
||
<span class="p">}</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">#define</span> <span class="pre">PY_SSIZE_T_CLEAN</span></code> was used to indicate that <code class="docutils literal notranslate"><span class="pre">Py_ssize_t</span></code> should be
|
||
used in some APIs instead of <code class="docutils literal notranslate"><span class="pre">int</span></code>.
|
||
It is not necessary since Python 3.13, but we keep it here for backward compatibility.
|
||
See <a class="reference internal" href="../c-api/arg.html#arg-parsing-string-and-buffers"><span class="std std-ref">Strings and buffers</span></a> for a description of this macro.</p>
|
||
</div>
|
||
<p>Setting <a class="reference internal" href="../c-api/init_config.html#c.PyConfig.program_name" title="PyConfig.program_name"><code class="xref c c-member docutils literal notranslate"><span class="pre">PyConfig.program_name</span></code></a> should be called before
|
||
<a class="reference internal" href="../c-api/init.html#c.Py_InitializeFromConfig" title="Py_InitializeFromConfig"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_InitializeFromConfig()</span></code></a> to inform the interpreter about paths to Python run-time
|
||
libraries. Next, the Python interpreter is initialized with
|
||
<a class="reference internal" href="../c-api/init.html#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>, followed by the execution of a hard-coded Python script
|
||
that prints the date and time. Afterwards, the <a class="reference internal" href="../c-api/init.html#c.Py_FinalizeEx" title="Py_FinalizeEx"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_FinalizeEx()</span></code></a> call shuts
|
||
the interpreter down, followed by the end of the program. In a real program,
|
||
you may want to get the Python script from another source, perhaps a text-editor
|
||
routine, a file, or a database. Getting the Python code from a file can better
|
||
be done by using the <a class="reference internal" href="../c-api/veryhigh.html#c.PyRun_SimpleFile" title="PyRun_SimpleFile"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyRun_SimpleFile()</span></code></a> function, which saves you the
|
||
trouble of allocating memory space and loading the file contents.</p>
|
||
</section>
|
||
<section id="beyond-very-high-level-embedding-an-overview">
|
||
<span id="lower-level-embedding"></span><h2><span class="section-number">1.2. </span>Beyond Very High Level Embedding: An overview<a class="headerlink" href="#beyond-very-high-level-embedding-an-overview" title="Link to this heading">¶</a></h2>
|
||
<p>The high level interface gives you the ability to execute arbitrary pieces of
|
||
Python code from your application, but exchanging data values is quite
|
||
cumbersome to say the least. If you want that, you should use lower level calls.
|
||
At the cost of having to write more C code, you can achieve almost anything.</p>
|
||
<p>It should be noted that extending Python and embedding Python is quite the same
|
||
activity, despite the different intent. Most topics discussed in the previous
|
||
chapters are still valid. To show this, consider what the extension code from
|
||
Python to C really does:</p>
|
||
<ol class="arabic simple">
|
||
<li><p>Convert data values from Python to C,</p></li>
|
||
<li><p>Perform a function call to a C routine using the converted values, and</p></li>
|
||
<li><p>Convert the data values from the call from C to Python.</p></li>
|
||
</ol>
|
||
<p>When embedding Python, the interface code does:</p>
|
||
<ol class="arabic simple">
|
||
<li><p>Convert data values from C to Python,</p></li>
|
||
<li><p>Perform a function call to a Python interface routine using the converted
|
||
values, and</p></li>
|
||
<li><p>Convert the data values from the call from Python to C.</p></li>
|
||
</ol>
|
||
<p>As you can see, the data conversion steps are simply swapped to accommodate the
|
||
different direction of the cross-language transfer. The only difference is the
|
||
routine that you call between both data conversions. When extending, you call a
|
||
C routine, when embedding, you call a Python routine.</p>
|
||
<p>This chapter will not discuss how to convert data from Python to C and vice
|
||
versa. Also, proper use of references and dealing with errors is assumed to be
|
||
understood. Since these aspects do not differ from extending the interpreter,
|
||
you can refer to earlier chapters for the required information.</p>
|
||
</section>
|
||
<section id="pure-embedding">
|
||
<span id="id1"></span><h2><span class="section-number">1.3. </span>Pure Embedding<a class="headerlink" href="#pure-embedding" title="Link to this heading">¶</a></h2>
|
||
<p>The first program aims to execute a function in a Python script. Like in the
|
||
section about the very high level interface, the Python interpreter does not
|
||
directly interact with the application (but that will change in the next
|
||
section).</p>
|
||
<p>The code to run a function defined in a Python script is:</p>
|
||
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define PY_SSIZE_T_CLEAN</span>
|
||
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><Python.h></span>
|
||
|
||
<span class="kt">int</span>
|
||
<span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">argv</span><span class="p">[])</span>
|
||
<span class="p">{</span>
|
||
<span class="w"> </span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="n">pName</span><span class="p">,</span><span class="w"> </span><span class="o">*</span><span class="n">pModule</span><span class="p">,</span><span class="w"> </span><span class="o">*</span><span class="n">pFunc</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="n">pArgs</span><span class="p">,</span><span class="w"> </span><span class="o">*</span><span class="n">pValue</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">;</span>
|
||
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">argc</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">3</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="s">"Usage: call pythonfile funcname [args]</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
|
||
<span class="w"> </span><span class="n">Py_Initialize</span><span class="p">();</span>
|
||
<span class="w"> </span><span class="n">pName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyUnicode_DecodeFSDefault</span><span class="p">(</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
|
||
<span class="w"> </span><span class="cm">/* Error checking of pName left out */</span>
|
||
|
||
<span class="w"> </span><span class="n">pModule</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyImport_Import</span><span class="p">(</span><span class="n">pName</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pName</span><span class="p">);</span>
|
||
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">pModule</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">pFunc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyObject_GetAttrString</span><span class="p">(</span><span class="n">pModule</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">2</span><span class="p">]);</span>
|
||
<span class="w"> </span><span class="cm">/* pFunc is a new reference */</span>
|
||
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">pFunc</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n">PyCallable_Check</span><span class="p">(</span><span class="n">pFunc</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">pArgs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyTuple_New</span><span class="p">(</span><span class="n">argc</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">3</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">argc</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">pValue</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyLong_FromLong</span><span class="p">(</span><span class="n">atoi</span><span class="p">(</span><span class="n">argv</span><span class="p">[</span><span class="n">i</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="p">]));</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">pValue</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pArgs</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pModule</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"Cannot convert argument</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="cm">/* pValue reference stolen here: */</span>
|
||
<span class="w"> </span><span class="n">PyTuple_SetItem</span><span class="p">(</span><span class="n">pArgs</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">pValue</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="n">pValue</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyObject_CallObject</span><span class="p">(</span><span class="n">pFunc</span><span class="p">,</span><span class="w"> </span><span class="n">pArgs</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pArgs</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">pValue</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Result of call: %ld</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">PyLong_AsLong</span><span class="p">(</span><span class="n">pValue</span><span class="p">));</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pValue</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pFunc</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pModule</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">PyErr_Print</span><span class="p">();</span>
|
||
<span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="s">"Call failed</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">PyErr_Occurred</span><span class="p">())</span>
|
||
<span class="w"> </span><span class="n">PyErr_Print</span><span class="p">();</span>
|
||
<span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"Cannot find function </span><span class="se">\"</span><span class="s">%s</span><span class="se">\"\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">2</span><span class="p">]);</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="n">Py_XDECREF</span><span class="p">(</span><span class="n">pFunc</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="n">Py_DECREF</span><span class="p">(</span><span class="n">pModule</span><span class="p">);</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">PyErr_Print</span><span class="p">();</span>
|
||
<span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"Failed to load </span><span class="se">\"</span><span class="s">%s</span><span class="se">\"\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">Py_FinalizeEx</span><span class="p">()</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">120</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="p">}</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>This code loads a Python script using <code class="docutils literal notranslate"><span class="pre">argv[1]</span></code>, and calls the function named
|
||
in <code class="docutils literal notranslate"><span class="pre">argv[2]</span></code>. Its integer arguments are the other values of the <code class="docutils literal notranslate"><span class="pre">argv</span></code>
|
||
array. If you <a class="reference internal" href="#compiling"><span class="std std-ref">compile and link</span></a> this program (let’s call
|
||
the finished executable <strong class="program">call</strong>), and use it to execute a Python
|
||
script, such as:</p>
|
||
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">multiply</span><span class="p">(</span><span class="n">a</span><span class="p">,</span><span class="n">b</span><span class="p">):</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s2">"Will compute"</span><span class="p">,</span> <span class="n">a</span><span class="p">,</span> <span class="s2">"times"</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
|
||
<span class="n">c</span> <span class="o">=</span> <span class="mi">0</span>
|
||
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">a</span><span class="p">):</span>
|
||
<span class="n">c</span> <span class="o">=</span> <span class="n">c</span> <span class="o">+</span> <span class="n">b</span>
|
||
<span class="k">return</span> <span class="n">c</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>then the result should be:</p>
|
||
<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>call<span class="w"> </span>multiply<span class="w"> </span>multiply<span class="w"> </span><span class="m">3</span><span class="w"> </span><span class="m">2</span>
|
||
<span class="go">Will compute 3 times 2</span>
|
||
<span class="go">Result of call: 6</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Although the program is quite large for its functionality, most of the code is
|
||
for data conversion between Python and C, and for error reporting. The
|
||
interesting part with respect to embedding Python starts with</p>
|
||
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">Py_Initialize</span><span class="p">();</span>
|
||
<span class="n">pName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyUnicode_DecodeFSDefault</span><span class="p">(</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
|
||
<span class="cm">/* Error checking of pName left out */</span>
|
||
<span class="n">pModule</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyImport_Import</span><span class="p">(</span><span class="n">pName</span><span class="p">);</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>After initializing the interpreter, the script is loaded using
|
||
<a class="reference internal" href="../c-api/import.html#c.PyImport_Import" title="PyImport_Import"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyImport_Import()</span></code></a>. This routine needs a Python string as its argument,
|
||
which is constructed using the <a class="reference internal" href="../c-api/unicode.html#c.PyUnicode_DecodeFSDefault" title="PyUnicode_DecodeFSDefault"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyUnicode_DecodeFSDefault()</span></code></a> data
|
||
conversion routine.</p>
|
||
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">pFunc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyObject_GetAttrString</span><span class="p">(</span><span class="n">pModule</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">2</span><span class="p">]);</span>
|
||
<span class="cm">/* pFunc is a new reference */</span>
|
||
|
||
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">pFunc</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n">PyCallable_Check</span><span class="p">(</span><span class="n">pFunc</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="p">...</span>
|
||
<span class="p">}</span>
|
||
<span class="n">Py_XDECREF</span><span class="p">(</span><span class="n">pFunc</span><span class="p">);</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Once the script is loaded, the name we’re looking for is retrieved using
|
||
<a class="reference internal" href="../c-api/object.html#c.PyObject_GetAttrString" title="PyObject_GetAttrString"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetAttrString()</span></code></a>. If the name exists, and the object returned is
|
||
callable, you can safely assume that it is a function. The program then
|
||
proceeds by constructing a tuple of arguments as normal. The call to the Python
|
||
function is then made with:</p>
|
||
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">pValue</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyObject_CallObject</span><span class="p">(</span><span class="n">pFunc</span><span class="p">,</span><span class="w"> </span><span class="n">pArgs</span><span class="p">);</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Upon return of the function, <code class="docutils literal notranslate"><span class="pre">pValue</span></code> is either <code class="docutils literal notranslate"><span class="pre">NULL</span></code> or it contains a
|
||
reference to the return value of the function. Be sure to release the reference
|
||
after examining the value.</p>
|
||
</section>
|
||
<section id="extending-embedded-python">
|
||
<span id="extending-with-embedding"></span><h2><span class="section-number">1.4. </span>Extending Embedded Python<a class="headerlink" href="#extending-embedded-python" title="Link to this heading">¶</a></h2>
|
||
<p>Until now, the embedded Python interpreter had no access to functionality from
|
||
the application itself. The Python API allows this by extending the embedded
|
||
interpreter. That is, the embedded interpreter gets extended with routines
|
||
provided by the application. While it sounds complex, it is not so bad. Simply
|
||
forget for a while that the application starts the Python interpreter. Instead,
|
||
consider the application to be a set of subroutines, and write some glue code
|
||
that gives Python access to those routines, just like you would write a normal
|
||
Python extension. For example:</p>
|
||
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">numargs</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span>
|
||
|
||
<span class="cm">/* Return the number of arguments of the application command line */</span>
|
||
<span class="k">static</span><span class="w"> </span><span class="n">PyObject</span><span class="o">*</span>
|
||
<span class="nf">emb_numargs</span><span class="p">(</span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="n">self</span><span class="p">,</span><span class="w"> </span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="n">args</span><span class="p">)</span>
|
||
<span class="p">{</span>
|
||
<span class="w"> </span><span class="k">if</span><span class="p">(</span><span class="o">!</span><span class="n">PyArg_ParseTuple</span><span class="p">(</span><span class="n">args</span><span class="p">,</span><span class="w"> </span><span class="s">":numargs"</span><span class="p">))</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nb">NULL</span><span class="p">;</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">PyLong_FromLong</span><span class="p">(</span><span class="n">numargs</span><span class="p">);</span>
|
||
<span class="p">}</span>
|
||
|
||
<span class="k">static</span><span class="w"> </span><span class="n">PyMethodDef</span><span class="w"> </span><span class="n">EmbMethods</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="p">{</span><span class="s">"numargs"</span><span class="p">,</span><span class="w"> </span><span class="n">emb_numargs</span><span class="p">,</span><span class="w"> </span><span class="n">METH_VARARGS</span><span class="p">,</span>
|
||
<span class="w"> </span><span class="s">"Return the number of arguments received by the process."</span><span class="p">},</span>
|
||
<span class="w"> </span><span class="p">{</span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">}</span>
|
||
<span class="p">};</span>
|
||
|
||
<span class="k">static</span><span class="w"> </span><span class="n">PyModuleDef</span><span class="w"> </span><span class="n">EmbModule</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span>
|
||
<span class="w"> </span><span class="n">PyModuleDef_HEAD_INIT</span><span class="p">,</span><span class="w"> </span><span class="s">"emb"</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="mi">-1</span><span class="p">,</span><span class="w"> </span><span class="n">EmbMethods</span><span class="p">,</span>
|
||
<span class="w"> </span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span>
|
||
<span class="p">};</span>
|
||
|
||
<span class="k">static</span><span class="w"> </span><span class="n">PyObject</span><span class="o">*</span>
|
||
<span class="nf">PyInit_emb</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span>
|
||
<span class="p">{</span>
|
||
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">PyModule_Create</span><span class="p">(</span><span class="o">&</span><span class="n">EmbModule</span><span class="p">);</span>
|
||
<span class="p">}</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Insert the above code just above the <code class="xref c c-func docutils literal notranslate"><span class="pre">main()</span></code> function. Also, insert the
|
||
following two statements before the call to <a class="reference internal" href="../c-api/init.html#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>:</p>
|
||
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">numargs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">argc</span><span class="p">;</span>
|
||
<span class="n">PyImport_AppendInittab</span><span class="p">(</span><span class="s">"emb"</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">PyInit_emb</span><span class="p">);</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>These two lines initialize the <code class="docutils literal notranslate"><span class="pre">numargs</span></code> variable, and make the
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">emb.numargs()</span></code> function accessible to the embedded Python interpreter.
|
||
With these extensions, the Python script can do things like</p>
|
||
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">emb</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s2">"Number of arguments"</span><span class="p">,</span> <span class="n">emb</span><span class="o">.</span><span class="n">numargs</span><span class="p">())</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>In a real application, the methods will expose an API of the application to
|
||
Python.</p>
|
||
</section>
|
||
<section id="embedding-python-in-c">
|
||
<span id="embeddingincplusplus"></span><h2><span class="section-number">1.5. </span>Embedding Python in C++<a class="headerlink" href="#embedding-python-in-c" title="Link to this heading">¶</a></h2>
|
||
<p>It is also possible to embed Python in a C++ program; precisely how this is done
|
||
will depend on the details of the C++ system used; in general you will need to
|
||
write the main program in C++, and use the C++ compiler to compile and link your
|
||
program. There is no need to recompile Python itself using C++.</p>
|
||
</section>
|
||
<section id="compiling-and-linking-under-unix-like-systems">
|
||
<span id="compiling"></span><h2><span class="section-number">1.6. </span>Compiling and Linking under Unix-like systems<a class="headerlink" href="#compiling-and-linking-under-unix-like-systems" title="Link to this heading">¶</a></h2>
|
||
<p>It is not necessarily trivial to find the right flags to pass to your
|
||
compiler (and linker) in order to embed the Python interpreter into your
|
||
application, particularly because Python needs to load library modules
|
||
implemented as C dynamic extensions (<code class="file docutils literal notranslate"><span class="pre">.so</span></code> files) linked against
|
||
it.</p>
|
||
<p>To find out the required compiler and linker flags, you can execute the
|
||
<code class="file docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X.Y</span></em><span class="pre">-config</span></code> script which is generated as part of the
|
||
installation process (a <code class="file docutils literal notranslate"><span class="pre">python3-config</span></code> script may also be
|
||
available). This script has several options, of which the following will
|
||
be directly useful to you:</p>
|
||
<ul>
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">pythonX.Y-config</span> <span class="pre">--cflags</span></code> will give you the recommended flags when
|
||
compiling:</p>
|
||
<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>/opt/bin/python3.11-config<span class="w"> </span>--cflags
|
||
<span class="go">-I/opt/include/python3.11 -I/opt/include/python3.11 -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall</span>
|
||
</pre></div>
|
||
</div>
|
||
</li>
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">pythonX.Y-config</span> <span class="pre">--ldflags</span> <span class="pre">--embed</span></code> will give you the recommended flags
|
||
when linking:</p>
|
||
<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>/opt/bin/python3.11-config<span class="w"> </span>--ldflags<span class="w"> </span>--embed
|
||
<span class="go">-L/opt/lib/python3.11/config-3.11-x86_64-linux-gnu -L/opt/lib -lpython3.11 -lpthread -ldl -lutil -lm</span>
|
||
</pre></div>
|
||
</div>
|
||
</li>
|
||
</ul>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>To avoid confusion between several Python installations (and especially
|
||
between the system Python and your own compiled Python), it is recommended
|
||
that you use the absolute path to <code class="file docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X.Y</span></em><span class="pre">-config</span></code>, as in the above
|
||
example.</p>
|
||
</div>
|
||
<p>If this procedure doesn’t work for you (it is not guaranteed to work for
|
||
all Unix-like platforms; however, we welcome <a class="reference internal" href="../bugs.html#reporting-bugs"><span class="std std-ref">bug reports</span></a>)
|
||
you will have to read your system’s documentation about dynamic linking and/or
|
||
examine Python’s <code class="file docutils literal notranslate"><span class="pre">Makefile</span></code> (use <a class="reference internal" href="../library/sysconfig.html#sysconfig.get_makefile_filename" title="sysconfig.get_makefile_filename"><code class="xref py py-func docutils literal notranslate"><span class="pre">sysconfig.get_makefile_filename()</span></code></a>
|
||
to find its location) and compilation
|
||
options. In this case, the <a class="reference internal" href="../library/sysconfig.html#module-sysconfig" title="sysconfig: Python's configuration information"><code class="xref py py-mod docutils literal notranslate"><span class="pre">sysconfig</span></code></a> module is a useful tool to
|
||
programmatically extract the configuration values that you will want to
|
||
combine together. For example:</p>
|
||
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">sysconfig</span>
|
||
<span class="gp">>>> </span><span class="n">sysconfig</span><span class="o">.</span><span class="n">get_config_var</span><span class="p">(</span><span class="s1">'LIBS'</span><span class="p">)</span>
|
||
<span class="go">'-lpthread -ldl -lutil'</span>
|
||
<span class="gp">>>> </span><span class="n">sysconfig</span><span class="o">.</span><span class="n">get_config_var</span><span class="p">(</span><span class="s1">'LINKFORSHARED'</span><span class="p">)</span>
|
||
<span class="go">'-Xlinker -export-dynamic'</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
</section>
|
||
|
||
|
||
<div class="clearer"></div>
|
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</div>
|
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|
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<div class="sphinxsidebar" role="navigation" aria-label="Main">
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<div class="sphinxsidebarwrapper">
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<div>
|
||
<h3><a href="../contents.html">Table of Contents</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#">1. Embedding Python in Another Application</a><ul>
|
||
<li><a class="reference internal" href="#very-high-level-embedding">1.1. Very High Level Embedding</a></li>
|
||
<li><a class="reference internal" href="#beyond-very-high-level-embedding-an-overview">1.2. Beyond Very High Level Embedding: An overview</a></li>
|
||
<li><a class="reference internal" href="#pure-embedding">1.3. Pure Embedding</a></li>
|
||
<li><a class="reference internal" href="#extending-embedded-python">1.4. Extending Embedded Python</a></li>
|
||
<li><a class="reference internal" href="#embedding-python-in-c">1.5. Embedding Python in C++</a></li>
|
||
<li><a class="reference internal" href="#compiling-and-linking-under-unix-like-systems">1.6. Compiling and Linking under Unix-like systems</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
|
||
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|
||
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|
||
<h4>Previous topic</h4>
|
||
<p class="topless"><a href="windows.html"
|
||
title="previous chapter"><span class="section-number">5. </span>Building C and C++ Extensions on Windows</a></p>
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|
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<h4>Next topic</h4>
|
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<li><a href="../bugs.html">Report a Bug</a></li>
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