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

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<head>

<title>1. 在其它 App 內嵌入 Python — Python 3.7.0 說明文件</title>

title="在 Python 3.7.0 說明文件中搜尋"

href="../_static/opensearch.xml"/>

</head><body>

<ul>

<a href="../genindex.html" title="General Index"

accesskey="I">索引</a></li>

<a href="../py-modindex.html" title="Python 模組索引"

>模組</a> |</li>

<a href="../c-api/index.html" title="Python / C API 參考手冊"

accesskey="N">下一頁</a> |</li>

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3.7.0

<a href="../index.html">Documentation </a> »

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<li class="nav-item nav-item-1"><a href="index.html" accesskey="U">Extending and Embedding the Python Interpreter</a> »</li>

</form>

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</div>

<h1>1. 在其它 App 內嵌入 Python<a class="headerlink" href="#embedding-python-in-another-application" title="本標題的永久連結">¶</a></h1>

The previous chapters discussed how to extend Python, that is, how to extend the

functionality of Python by attaching a library of C functions to it. It is also

possible to do it the other way around: enrich your C/C++ application by

embedding Python in it. Embedding provides your application with the ability to

implement some of the functionality of your application in Python rather than C

or C++. This can be used for many purposes; one example would be to allow users

to tailor the application to their needs by writing some scripts in Python. You

can also use it yourself if some of the functionality can be written in Python

more easily.

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

to do with Python — instead, some parts of the application occasionally call

the Python interpreter to run some Python code.

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">Py_Initialize()</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.

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">PyRun_SimpleString()</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">PyRun_SimpleFile()</code></a>. You can also call the lower-level operations

described in the previous chapters to construct and use Python objects.

也參考

<dt><a class="reference internal" href="../c-api/index.html#c-api-index">Python / C API 參考手冊</a></dt>

<dd>The details of Python’s C interface are given in this manual. A great deal of

necessary information can be found here.</dd>

</dl>

</div>

<h2>1.1. Very High Level Embedding<a class="headerlink" href="#very-high-level-embedding" title="本標題的永久連結">¶</a></h2>

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.

<div class="highlight-c notranslate"><div class="highlight"><pre>#include <Python.h>

int

main(int argc, char *argv[])

{

wchar_t *program = Py_DecodeLocale(argv[0], NULL);

if (program == NULL) {

fprintf(stderr, "Fatal error: cannot decode argv[0]\n");

exit(1);

}

Py_SetProgramName(program); /* optional but recommended */

Py_Initialize();

PyRun_SimpleString("from time import time,ctime\n"

"print('Today is', ctime(time()))\n");

if (Py_FinalizeEx() < 0) {

exit(120);

}

PyMem_RawFree(program);

return 0;

}

</pre></div>

</div>

The <a class="reference internal" href="../c-api/init.html#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate">Py_SetProgramName()</code></a> function should be called before

<a class="reference internal" href="../c-api/init.html#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate">Py_Initialize()</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">Py_Initialize()</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">Py_FinalizeEx()</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">PyRun_SimpleFile()</code></a> function, which saves you the

trouble of allocating memory space and loading the file contents.

</div>

<h2>1.2. Beyond Very High Level Embedding: An overview<a class="headerlink" href="#beyond-very-high-level-embedding-an-overview" title="本標題的永久連結">¶</a></h2>

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.

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:

<li>Convert data values from Python to C,</li>

<li>Perform a function call to a C routine using the converted values, and</li>

<li>Convert the data values from the call from C to Python.</li>

</ol>

When embedding Python, the interface code does:

<li>Convert data values from C to Python,</li>

<li>Perform a function call to a Python interface routine using the converted

values, and</li>

<li>Convert the data values from the call from Python to C.</li>

</ol>

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.

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.

</div>

<h2>1.3. Pure Embedding<a class="headerlink" href="#pure-embedding" title="本標題的永久連結">¶</a></h2>

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).

The code to run a function defined in a Python script is:

<div class="highlight-c notranslate"><div class="highlight"><pre>#include <Python.h>

int

{

PyObject *pName, *pModule, *pFunc;

PyObject *pArgs, *pValue;

int i;

if (argc < 3) {

fprintf(stderr,"Usage: call pythonfile funcname [args]\n");

return 1;

}

Py_Initialize();

pName = PyUnicode_DecodeFSDefault(argv[1]);

/* Error checking of pName left out */

pModule = PyImport_Import(pName);

Py_DECREF(pName);

if (pModule != NULL) {

pFunc = PyObject_GetAttrString(pModule, argv[2]);

/* pFunc is a new reference */

if (pFunc && PyCallable_Check(pFunc)) {

pArgs = PyTuple_New(argc - 3);

for (i = 0; i < argc - 3; ++i) {

pValue = PyLong_FromLong(atoi(argv[i + 3]));

if (!pValue) {

Py_DECREF(pArgs);

Py_DECREF(pModule);

fprintf(stderr, "Cannot convert argument\n");

return 1;

}

/* pValue reference stolen here: */

PyTuple_SetItem(pArgs, i, pValue);

}

pValue = PyObject_CallObject(pFunc, pArgs);

Py_DECREF(pArgs);

if (pValue != NULL) {

printf("Result of call: %ld\n", PyLong_AsLong(pValue));

Py_DECREF(pValue);

}

else {

Py_DECREF(pFunc);

Py_DECREF(pModule);

PyErr_Print();

fprintf(stderr,"Call failed\n");

return 1;

}

else {

if (PyErr_Occurred())

PyErr_Print();

fprintf(stderr, "Cannot find function \"%s\"\n", argv[2]);

}

Py_XDECREF(pFunc);

Py_DECREF(pModule);

}

else {

PyErr_Print();

fprintf(stderr, "Failed to load \"%s\"\n", argv[1]);

return 1;

}

return 120;

}

return 0;

}

</pre></div>

</div>

This code loads a Python script using <code class="docutils literal notranslate">argv[1]</code>, and calls the function named

in <code class="docutils literal notranslate">argv[2]</code>. Its integer arguments are the other values of the <code class="docutils literal notranslate">argv</code>

array. If you <a class="reference internal" href="#compiling">compile and link</a> this program (let’s call

the finished executable call), and use it to execute a Python

script, such as:

<div class="highlight-python notranslate"><div class="highlight"><pre>def multiply(a,b):

print("Will compute", a, "times", b)

c = 0

for i in range(0, a):

c = c + b

return c

</pre></div>

</div>

then the result should be:

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ call multiply multiply 3 2

Will compute 3 times 2

Result of call: 6

</pre></div>

</div>

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

<div class="highlight-c notranslate"><div class="highlight"><pre>Py_Initialize();

/* Error checking of pName left out */

pModule = PyImport_Import(pName);

</pre></div>

</div>

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">PyImport_Import()</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_FromString" title="PyUnicode_FromString"><code class="xref c c-func docutils literal notranslate">PyUnicode_FromString()</code></a> data conversion

routine.

<div class="highlight-c notranslate"><div class="highlight"><pre>pFunc = PyObject_GetAttrString(pModule, argv[2]);

/* pFunc is a new reference */

...

}

Py_XDECREF(pFunc);

</pre></div>

</div>

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">PyObject_GetAttrString()</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:

<div class="highlight-c notranslate"><div class="highlight"><pre>pValue = PyObject_CallObject(pFunc, pArgs);

</pre></div>

</div>

Upon return of the function, <code class="docutils literal notranslate">pValue</code> is either NULL or it contains a

reference to the return value of the function. Be sure to release the reference

after examining the value.

</div>

<h2>1.4. Extending Embedded Python<a class="headerlink" href="#extending-embedded-python" title="本標題的永久連結">¶</a></h2>

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:

<div class="highlight-c notranslate"><div class="highlight"><pre>static int numargs=0;

/* Return the number of arguments of the application command line */

static PyObject*

emb_numargs(PyObject *self, PyObject *args)

{

if(!PyArg_ParseTuple(args, ":numargs"))

return NULL;

return PyLong_FromLong(numargs);

}

static PyMethodDef EmbMethods[] = {

{"numargs", emb_numargs, METH_VARARGS,

"Return the number of arguments received by the process."},

{NULL, NULL, 0, NULL}

};

static PyModuleDef EmbModule = {

PyModuleDef_HEAD_INIT, "emb", NULL, -1, EmbMethods,

NULL, NULL, NULL, NULL

};

static PyObject*

PyInit_emb(void)

{

return PyModule_Create(&EmbModule);

}

</pre></div>

</div>

Insert the above code just above the <code class="xref c c-func docutils literal notranslate">main()</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">Py_Initialize()</code></a>:

<div class="highlight-c notranslate"><div class="highlight"><pre>numargs = argc;

PyImport_AppendInittab("emb", &PyInit_emb);

</pre></div>

</div>

These two lines initialize the <code class="docutils literal notranslate">numargs</code> variable, and make the

<code class="xref py py-func docutils literal notranslate">emb.numargs()</code> function accessible to the embedded Python interpreter.

With these extensions, the Python script can do things like

<div class="highlight-python notranslate"><div class="highlight"><pre>import emb

print("Number of arguments", emb.numargs())

</pre></div>

</div>

In a real application, the methods will expose an API of the application to

Python.

</div>

<h2>1.5. Embedding Python in C++<a class="headerlink" href="#embedding-python-in-c" title="本標題的永久連結">¶</a></h2>

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++.

</div>

<h2>1.6. Compiling and Linking under Unix-like systems<a class="headerlink" href="#compiling-and-linking-under-unix-like-systems" title="本標題的永久連結">¶</a></h2>

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">.so</code> files) linked against

it.

To find out the required compiler and linker flags, you can execute the

<code class="file docutils literal notranslate">pythonX.Y-config</code> script which is generated as part of the

installation process (a <code class="file docutils literal notranslate">python3-config</code> script may also be

available). This script has several options, of which the following will

be directly useful to you:

<ul>

<li><code class="docutils literal notranslate">pythonX.Y-config --cflags</code> will give you the recommended flags when

compiling:

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ /opt/bin/python3.4-config --cflags

-I/opt/include/python3.4m -I/opt/include/python3.4m -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes

</pre></div>

</div>

</li>

<li><code class="docutils literal notranslate">pythonX.Y-config --ldflags</code> will give you the recommended flags when

linking:

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ /opt/bin/python3.4-config --ldflags

-L/opt/lib/python3.4/config-3.4m -lpthread -ldl -lutil -lm -lpython3.4m -Xlinker -export-dynamic

</pre></div>

</div>

</li>

</ul>

備註

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">pythonX.Y-config</code>, as in the above

example.

</div>

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">bug reports</a>)

you will have to read your system’s documentation about dynamic linking and/or

examine Python’s <code class="file docutils literal notranslate">Makefile</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">sysconfig.get_makefile_filename()</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">sysconfig</code></a> module is a useful tool to

programmatically extract the configuration values that you will want to

combine together. For example:

<div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> import sysconfig

>>> sysconfig.get_config_var('LIBS')

'-lpthread -ldl -lutil'

>>> sysconfig.get_config_var('LINKFORSHARED')

'-Xlinker -export-dynamic'

</pre></div>

</div>

<ul>

<li><a class="reference internal" href="#">1. 在其它 App 內嵌入 Python</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>

<a href="windows.html"

title="上一章">5. Building C and C++ Extensions on Windows</a>

<a href="../c-api/index.html"

title="下一章">Python / C API 參考手冊</a>

<li><a href="../bugs.html">Report a Bug</a></li>

<li>

<a href="https://github.com/python/cpython/blob/3.7/Doc/extending/embedding.rst"

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</a>

</li>

</ul>

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