Loading DLL's in Python

Question

I'm following the guide found here:

http://www.dalkescientific.com/writings/NBN/c_extensions.html

for creating C extensions to python. But when I try to run any python program after building that module, such as the first one listed or mandelbrot.py (listed towards the end of the page). I get the error on the line libc = ctypes.CDLL("libc.dylib", ctypes.RTLD_GLOBAL)

The error is:

Traceback (most recent call last):
File "cos.py", line 5, in < module >
libc = ctypes.CDLL("libc.dylib", ctypes.RTLD_GLOBAL)
File "/usr/lib/python2.7/ctypes/__init__.py", line 365, in __init__
self._handle = _dlopen(self._name, mode)
OSError: libc.dylib: cannot open shared object file: No such file or directory

I'm using Linux so I'm not sure if that is the problem. And if it is, how would I accomplish this on Linux? I know dll is how Windows refers to shared objects. But does the syntax change? I can't seem to find an answer anywhere.

When showing tracebacks like this put them in a codeblock to avoid this issue. — phantom
– phantom, Commented Oct 31, 2014 at 19:42
I should've do it considering it's pretty obvious to put tracebacks in a code block. I must've been in a rush at work and forgotten. My apologies. — ss7
– ss7, Commented Jan 8, 2015 at 5:51

Lars Ljung · Accepted Answer · 2014-10-31 20:42:12Z

1

On GNU/Linux the cos() function is located in a library called libm.so. So you need to replace "libc.dylib" with "libm.so".

answered Oct 31, 2014 at 20:42

Lars Ljung

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2 Comments

ss7 Over a year ago

Sorry I'm an idiot, where do I replace that file exactly? Where is libc.dylib typically located? And what's the most reliable way to get a clean copy of libm.so?

Lars Ljung Over a year ago

No, you shouldn't replace any files on your system. Just change the code to ctypes.CDLL("libm.so", ctypes.RTLD_GLOBAL) instead of ctypes.CDLL("libc.dylib", ctypes.RTLD_GLOBAL).

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