Python C extension: Use extension PYD or DLL?
Question:
I have a Python extension written in C and I wonder if I should use the file extension DLL or PYD under Windows. (And what would I use in Linux?)
Are there any differences (besides the filename)?
I found an unofficial article. Is this the secret of pyc?
Why can’t I find any official article on this topic?
Answers:
Presuming your Python extension foo is intended to be used as a module, accessible via import foo, you don’t need to know what the filename extension should be on what operating system. You just use distutils. You will get a .pyd on Windows, and a .so on Linux etc. Read this documentation.
Update in response to comment by @gecco
import foo is working both both extension types: dll and pyd. The extension does not matter here… :
For me (Python 2.7.1, Windows 7), python -vv shows only pyd, py, pyw and pyc extensions (in that order) being searched. If I have foo.pyd in C:python27libsite-packages, import foo works. If I rename that file to foo.dll, import foo fails.
pyd files are just dll files ready for python importing.
To distinguish them from normal dlls, I recommend .pyd not .dll in windows.
Here is the official doc about this issue:
http://docs.python.org/faq/windows.html#is-a-pyd-file-the-same-as-a-dll
In Windows you can use *.pyd to be imported directly from Python import foo but for *.dll you should use this:
from ctypes import cdll
#load dll file , the file in the same .py file location or enter the full path
mylib=cdll.LoadLibrary("foo.dll")
#call a function from this dll (c-ext)
ReturnedValue=mylib.FunctionName()
If you want to explore what functions are exported in this Dll use this tool
UPDATE:
Here’s an example using distutils and SWIG to build the extension. Check this article out, it shows many simple examples under Windows and Linux.
According to the Creating Your Own Project step (Step 7 of “The Cookbook Approach”) of Building C and C++ Extensions on Windows
The output file should be called spam.pyd (in Release mode) or spam_d.pyd (in Debug mode). The extension .pyd was chosen to avoid confusion with a system library spam.dll to which your module could be a Python interface.
So a .pyd file is just a DLL renamed to save on confusion.
On linux however, speaking from experience it seems that you need to use the .so extension for python dlls. This is just a standard unix shared library. I can’t provide a source or reason for why python on linux does not change the file extension, however I can show you how to demonstrate it. At the shell, run the following:
python -vv
>>> import fakemodule
You’ll notice that the output shows:
trying /usr/lib/python2.5/site-packages/fakemodule.so
I have a Python extension written in C and I wonder if I should use the file extension DLL or PYD under Windows. (And what would I use in Linux?)
Are there any differences (besides the filename)?
I found an unofficial article. Is this the secret of pyc?
Why can’t I find any official article on this topic?
Presuming your Python extension foo is intended to be used as a module, accessible via import foo, you don’t need to know what the filename extension should be on what operating system. You just use distutils. You will get a .pyd on Windows, and a .so on Linux etc. Read this documentation.
Update in response to comment by @gecco
import foo is working both both extension types: dll and pyd. The extension does not matter here… :
For me (Python 2.7.1, Windows 7), python -vv shows only pyd, py, pyw and pyc extensions (in that order) being searched. If I have foo.pyd in C:python27libsite-packages, import foo works. If I rename that file to foo.dll, import foo fails.
pyd files are just dll files ready for python importing.
To distinguish them from normal dlls, I recommend .pyd not .dll in windows.
Here is the official doc about this issue:
http://docs.python.org/faq/windows.html#is-a-pyd-file-the-same-as-a-dll
In Windows you can use *.pyd to be imported directly from Python import foo but for *.dll you should use this:
from ctypes import cdll
#load dll file , the file in the same .py file location or enter the full path
mylib=cdll.LoadLibrary("foo.dll")
#call a function from this dll (c-ext)
ReturnedValue=mylib.FunctionName()
If you want to explore what functions are exported in this Dll use this tool
UPDATE:
Here’s an example using distutils and SWIG to build the extension. Check this article out, it shows many simple examples under Windows and Linux.
According to the Creating Your Own Project step (Step 7 of “The Cookbook Approach”) of Building C and C++ Extensions on Windows
The output file should be called spam.pyd (in Release mode) or spam_d.pyd (in Debug mode). The extension .pyd was chosen to avoid confusion with a system library spam.dll to which your module could be a Python interface.
So a .pyd file is just a DLL renamed to save on confusion.
On linux however, speaking from experience it seems that you need to use the .so extension for python dlls. This is just a standard unix shared library. I can’t provide a source or reason for why python on linux does not change the file extension, however I can show you how to demonstrate it. At the shell, run the following:
python -vv
>>> import fakemodule
You’ll notice that the output shows:
trying /usr/lib/python2.5/site-packages/fakemodule.so