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Extending and Embedding the Python Interpreter |
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4.1 A Cookbook Approach
There are two approaches to building extension modules on Windows,
just as there are on Unix: use the
distutils package to
control the build process, or do things manually. The distutils
approach works well for most extensions; documentation on using
distutils to build and
package extension modules is available in
Distributing Python Modules. This
section describes the manual approach to building Python extensions
written in C or C++.
To build extensions using these instructions, you need to have a copy
of the Python sources of the same version as your installed Python.
You will need Microsoft Visual C++ ``Developer Studio''; project
files are supplied for VC++ version 7.1, but you can use older
versions of VC++. Notice that you should use the same version of
VC++that was used to build Python itself. The example files
described here are distributed with the Python sources in the
PC\example_nt\ directory.
- Copy the example files
The example_nt directory is a subdirectory of the PC
directory, in order to keep all the PC-specific files under the
same directory in the source distribution. However, the
example_nt directory can't actually be used from this
location. You first need to copy or move it up one level, so that
example_nt is a sibling of the PC and Include
directories. Do all your work from within this new location.
- Open the project
From VC++, use the File > Open Solution
dialog (not File > Open!). Navigate to and
select the file example.sln, in the copy of the
example_nt directory you made above. Click Open.
- Build the example DLL
In order to check that everything is set up right, try building:
- Select a configuration. This step is optional. Choose
Build > Configuration Manager > Active
Solution Configuration and select either Release
orDebug. If you skip this step,
VC++ will use the Debug configuration by default.
- Build the DLL. Choose Build > Build
Solution. This creates all intermediate and result files in
a subdirectory called either Debug or Release,
depending on which configuration you selected in the preceding
step.
- Testing the debug-mode DLL
Once the Debug build has succeeded, bring up a DOS box, and change
to the example_nt\Debug directory. You
should now be able to repeat the following session (C> is
the DOS prompt, >>> is the Python prompt; note that
build information and various debug output from Python may not
match this screen dump exactly):
C>..\..\PCbuild\python_d
Adding parser accelerators ...
Done.
Python 2.2 (#28, Dec 19 2001, 23:26:37) [MSC 32 bit (Intel)] on win32
Type "copyright", "credits" or "license" for more information.
>>> import example
[4897 refs]
>>> example.foo()
Hello, world
[4903 refs]
>>>
Congratulations! You've successfully built your first Python
extension module.
- Creating your own project
Choose a name and create a directory for it. Copy your C sources
into it. Note that the module source file name does not
necessarily have to match the module name, but the name of the
initialization function should match the module name -- you can
only import a module spam if its initialization function
is called initspam(), and it should call
Py_InitModule() with the string "spam" as its
first argument (use the minimal example.c in this directory
as a guide). By convention, it lives in a file called
spam.c or spammodule.c. The output file should be
called spam.dll or spam.pyd (the latter is supported
to avoid confusion with a system library spam.dll to which
your module could be a Python interface) in Release mode, or
spam_d.dll or spam_d.pyd in Debug mode.
Now your options are:
- Copy example.sln and example.vcproj, rename
them to spam.*, and edit them by hand, or
- Create a brand new project; instructions are below.
In either case, copy example_nt\example.def
to spam\spam.def, and edit the new
spam.def so its second line contains the string
`initspam '. If you created a new project yourself, add the
file spam.def to the project now. (This is an annoying
little file with only two lines. An alternative approach is to
forget about the .def file, and add the option
/export:initspam somewhere to the Link settings, by
manually editing the setting in Project Properties dialog).
- Creating a brand new project
Use the File > New > Project dialog to
create a new Project Workspace. Select Visual C++
Projects/Win32/ Win32 Project, enter the name ("spam"), and
make sure the Location is set to parent of the spam
directory you have created (which should be a direct subdirectory
of the Python build tree, a sibling of Include and
PC). Select Win32 as the platform (in my version, this is
the only choice). Make sure the Create new workspace radio button
is selected. Click OK.
You should now create the file spam.def as instructed in
the previous section. Add the source files to the project, using
Project > Add Existing Item. Set the pattern to
*.* and select both spam.c and spam.def and
click OK. (Inserting them one by one is fine too.)
Now open the Project > spam properties dialog.
You only need to change a few settings. Make sure All
Configurations is selected from the Settings for:
dropdown list. Select the C/C++ tab. Choose the General
category in the popup menu at the top. Type the following text in
the entry box labeled Additional Include Directories:
Then, choose the General category in the Linker tab, and enter
in the text box labelled Additional library Directories.
Now you need to add some mode-specific settings:
Select Release in the Configuration
dropdown list. Choose the Link tab, choose the
Input category, and append pythonXY.lib to the
list in the Additional Dependencies box.
Select Debug in the Configuration dropdown
list, and append pythonXY_d.lib to the list in the
Additional Dependencies box. Then click the C/C++
tab, select Code Generation, and select
Multi-threaded Debug DLL from the Runtime
library dropdown list.
Select Release again from the Configuration
dropdown list. Select Multi-threaded DLL from the
Runtime library dropdown list.
If your module creates a new type, you may have trouble with this line:
PyObject_HEAD_INIT(&PyType_Type)
Change it to:
and add the following to the module initialization function:
MyObject_Type.ob_type = &PyType_Type;
Refer to section 3 of the
Python FAQ for details
on why you must do this.
Release 2.5.2, documentation updated on 21st February, 2008.
See About this document... for information on suggesting changes.
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