Python CFFI module fails when loading dll: OSError 0x7e

Question

I run Python 3.3 (Anaconda distribution) under Windows 7, 64-bit. I have attempted to install the Weasyprint app/library, which has a number of dependencies, including CFFI, which I had to compile from source because no compatible version of it was available in a binary distribution.

When I run weasyprint, it chokes during the import loading process, specifically when it calls CFFI in order to load the GTK+ library dll for Cairo. The error that I get is as follows:

$ weasyprint
Traceback (most recent call last):
  File "c:\anaconda\envs\py33\lib\site-packages\cffi-0.8-py3.3-win-amd64.egg\cffi\api.py", line 399, in _make_ffi_library
    backendlib = backend.load_library(name, flags)
OSError: cannot load library libcairo-2.dll: error 0x7e

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Anaconda\envs\py33\Scripts\weasyprint-script.py", line 9, in <module>
    load_entry_point('WeasyPrint==0.20', 'console_scripts', 'weasyprint')()
  File "C:\Anaconda\envs\py33\lib\site-packages\pkg_resources.py", line 343, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "C:\Anaconda\envs\py33\lib\site-packages\pkg_resources.py", line 2355, in load_entry_point
    return ep.load()
  File "C:\Anaconda\envs\py33\lib\site-packages\pkg_resources.py", line 2061, in load
    entry = __import__(self.module_name, globals(),globals(), ['__name__'])
  File "c:\anaconda\envs\py33\lib\site-packages\weasyprint-0.20-py3.3.egg\weasyprint\__init__.py", line 309, in <module>
    from .css import PARSER, preprocess_stylesheet
  File "c:\anaconda\envs\py33\lib\site-packages\weasyprint-0.20-py3.3.egg\weasyprint\css\__init__.py", line 30, in <module>
    from . import computed_values
  File "c:\anaconda\envs\py33\lib\site-packages\weasyprint-0.20-py3.3.egg\weasyprint\css\computed_values.py", line 18, in <module>
    from .. import text
  File "c:\anaconda\envs\py33\lib\site-packages\weasyprint-0.20-py3.3.egg\weasyprint\text.py", line 18, in <module>
    import cairocffi as cairo
  File "c:\anaconda\envs\py33\lib\site-packages\cairocffi-0.5.1-py3.3.egg\cairocffi\__init__.py", line 39, in <module>
    cairo = dlopen(ffi, 'libcairo-2.dll', 'cairo', 'libcairo-2')
  File "c:\anaconda\envs\py33\lib\site-packages\cairocffi-0.5.1-py3.3.egg\cairocffi\__init__.py", line 34, in dlopen
    return ffi.dlopen(names[0])  # pragma: no cover
  File "c:\anaconda\envs\py33\lib\site-packages\cffi-0.8-py3.3-win-amd64.egg\cffi\api.py", line 117, in dlopen
    lib, function_cache = _make_ffi_library(self, name, flags)
  File "c:\anaconda\envs\py33\lib\site-packages\cffi-0.8-py3.3-win-amd64.egg\cffi\api.py", line 405, in _make_ffi_library
    backendlib = backend.load_library(path, flags)
OSError: cannot load library C:\Windows\system32\libcairo-2.dll: error 0x7e 

The environment I have is as follows: Windows 7.1 64-bit, Python 3.3 64 bit, CFFI compiled (by me) under Visual Studio 2010 with a 64-bit environment, and Cairo's libcairo-2.dll also in a 64-bit version.

I am not a Windows programmer, and am only delving into this mess because I want to get Weasyprint to work for another (Python language) project. I have done a minor bit of Windows programming a long time ago under Delphi, so I have a vague grasp of how this stuff works, but I have been unable to solve this problem.

Prot

Did you solve the problem at the end? I am facing the same error and have no idea where to start fixing it. Any suggestion is appreciated. Thank you! – Dominant

The problem is that CFFI has to be compiled with Visual Studio, because the DLLs have to be compatible with Python, which was compiled under that toolchain. I had VS 2010 Express, which comes with C++, but CFFI was designed to be compiled under VS 2007, if I remember correctly, and Microsoft changed its make system so you can't use vsbuild anymore (or something like that that was equally annoying). Apparently the MS world isn't like the *nix world, where your toolchain from 2014 still pretty much compiles code from 1986. So I was SOL... I run weasyprint on a Mac box to get around the issue. – Prot

Answer 1

I was getting similar errors (conflicting DLLs) and it was finally resolved simply by moving the path to GTK (ex: "C:\gtk\bin") to the beginning of my environment variables.

Spirketing

And don't try to use "C:\gtk+\bin". It doesn't like spaces or the + in the path. – Justajustemilieu

This didn't work for me. I still get the error 'OSError: dlopen() failed to load a library: cairo / cairo-2' – Resect

@Resect - my guess is you're missing some dependencies. I think I used this tool dependencywalker.com to find some things I was missing. I think the versions that worked for me were pycairo-1.8.10.win32-py2.7.exe and gtk+-bundle_2.22.1-20101229_win64.zip . Hope it helps. – Spirketing

thanks for the dependency walker suggestion. I got this output when selecting weasyprint.exe Error: At least one required implicit or forwarded dependency was not found. < Warning: At least one delay-load dependency module was not found. Warning: At least one module has an unresolved import due to a missing export function in a delay-load dependent module. > I'm not sure how to interpret that – Resect

Thanks, this helped. I think the issue was a space in my install directory (but I also moved the path to the beginning of my environment variables), annoying how fragile this is. – Udo

Answer 2

Installing GTK+ didn't work for me. I solved this problem using UniConverter2.0. My environments is

• Python 3.7
• Windows 10 x64

1. Install uniconvertor-2.0rc4-win64_headless.msi,
2. Find the "dll" sub-directory under the UniConverter installation path.(In my case, C:\Program Files\UniConvertor-2.0rc4\dlls)
3. Add this "dll" path to the system path.
4. Close VSCode(or other) and reopen the project.
5. Try to run your code again. Enjoy!

Abisia