Cython compiled C extension: ImportError: dynamic module does not define init function
Question:
I have just compiled part of my C library as an extension using Cython, as a “proof of concept”. I managed to hack the code (const correctnes problems etc aside), to finally get an extension built.
However, when I attempted to import the newly created extension, I got the following error:
ImportError: dynamic module does not define init function
What am I doing wrong and how do I fix this?
I am using Cythn 0.11.2 and Python 2.6.5 on Ubuntu 10.0.4
Answers:
This is a very late answer – but I just had the same error, and mine went away when I used __cinit__ instead of __init__. I’m still learing about extension types so currently I do not know why this happens. 🙂 (You can take a look at http://docs.cython.org/src/reference/extension_types.html#initialization-cinit-and-init) Hope this is useful to someone.
It appears that it’s a bug/feature in Cython. I had the same thing, but simply added:
STUFF = "Hi"
to the top of my .pyx file and the issue went away. It appears if there is no global initialization (a cinit or setting a global variable), that the required initialization code isn’t generated.
I’ve found that a frequent cause of this problem is, when using a distutils setup file to compile the code, that the .pyx base name does not match the extension name, e.g:
ext = Extension(name='different', sources=['cython_ext.pyx']) # Won't work
To avoid the problem the extension name should be exactly the same, in this case, cython_ext.
Likewise a late answer… but I kept finding my way back to this question in particular. It probably is related to the mismatched names issue that Dologan addresses.
What happened in my case was that I was adapting an example I’d gotten to work, and got the module does not define init function error. This was verified by using (e.g.)
nm -m build/lib.macosx-10.9-x86_64-2.7/myproj.so
In this command’s output I searched for ‘init’ and found
000000000000c0d0 (__TEXT,__text) external _initexample
I had removed all instances of ‘example’ from my setup.py and .pyx file, but this persisted even after removing the extension from site-packages, removing the build and dist folders, etc. I finally found that the .cpp file being generated from my .pyx file was still referring to the class name in the example. Once I reran my setup.py, import works, and indeed the .so file includes
000000000000c0a0 (__TEXT,__text) external _initmyproj
This is solved by adding a doc-string to your functions.
Another really late answer in my case I had accidentally called cython in a terminal that was running python2, while trying to use the generated library from a terminal that was on another python environment, using python3.
Using the same python version everywhere fixed it.
I had the same error and was solved by running the main .py script in “Execute in a dedicated console ” mode. Available in Tools – Preferences – Run.
I solve it by
def cinit(self): pass
Hope it helps.
I’ve also ran into this problem. Make sure that your Cython file contains at least one of the following:
- a normal Python
def
- a normal Python class (not
cdef class)
- a line of Python initialization, eg.
a=None or a logger load
Otherwise Cython won’t generate a PyInit routine needed to load the module, and as such the module won’t be importable by Python.
I have just compiled part of my C library as an extension using Cython, as a “proof of concept”. I managed to hack the code (const correctnes problems etc aside), to finally get an extension built.
However, when I attempted to import the newly created extension, I got the following error:
ImportError: dynamic module does not define init function
What am I doing wrong and how do I fix this?
I am using Cythn 0.11.2 and Python 2.6.5 on Ubuntu 10.0.4
This is a very late answer – but I just had the same error, and mine went away when I used __cinit__ instead of __init__. I’m still learing about extension types so currently I do not know why this happens. 🙂 (You can take a look at http://docs.cython.org/src/reference/extension_types.html#initialization-cinit-and-init) Hope this is useful to someone.
It appears that it’s a bug/feature in Cython. I had the same thing, but simply added:
STUFF = "Hi"
to the top of my .pyx file and the issue went away. It appears if there is no global initialization (a cinit or setting a global variable), that the required initialization code isn’t generated.
I’ve found that a frequent cause of this problem is, when using a distutils setup file to compile the code, that the .pyx base name does not match the extension name, e.g:
ext = Extension(name='different', sources=['cython_ext.pyx']) # Won't work
To avoid the problem the extension name should be exactly the same, in this case, cython_ext.
Likewise a late answer… but I kept finding my way back to this question in particular. It probably is related to the mismatched names issue that Dologan addresses.
What happened in my case was that I was adapting an example I’d gotten to work, and got the module does not define init function error. This was verified by using (e.g.)
nm -m build/lib.macosx-10.9-x86_64-2.7/myproj.so
In this command’s output I searched for ‘init’ and found
000000000000c0d0 (__TEXT,__text) external _initexample
I had removed all instances of ‘example’ from my setup.py and .pyx file, but this persisted even after removing the extension from site-packages, removing the build and dist folders, etc. I finally found that the .cpp file being generated from my .pyx file was still referring to the class name in the example. Once I reran my setup.py, import works, and indeed the .so file includes
000000000000c0a0 (__TEXT,__text) external _initmyproj
This is solved by adding a doc-string to your functions.
Another really late answer in my case I had accidentally called cython in a terminal that was running python2, while trying to use the generated library from a terminal that was on another python environment, using python3.
Using the same python version everywhere fixed it.
I had the same error and was solved by running the main .py script in “Execute in a dedicated console ” mode. Available in Tools – Preferences – Run.
I solve it by
def cinit(self): pass
Hope it helps.
I’ve also ran into this problem. Make sure that your Cython file contains at least one of the following:
- a normal Python
def - a normal Python class (not
cdef class) - a line of Python initialization, eg.
a=Noneor a logger load
Otherwise Cython won’t generate a PyInit routine needed to load the module, and as such the module won’t be importable by Python.