Wednesday, July 27, 2016

Error: Fatal Python error: PyThreadState_Get: no current thread in Caffe (PyCaffe)

import caffe

Following error is encountered (and Python crashes) when executing the above import statement in Python. (PyCaffe)

Fatal Python error: PyThreadState_Get: no current thread

Usually, the error is due to the conflicts between different Python versions installed in the machine. If you tried the following step (re install), as mentioned in many other posts and still get the error, then try the trouble shooting steps that I have mentioned in this post. They worked for me :)

brew uninstall boost-python
brew install --build-from-source --fresh -vd boost-python

Caffe is primarily written in C++ and PyCaffe is it's Python interface. PyCaffe uses Boost Python
which is a C++ library to enable interoperability between C++ and the Python.

During the Caffe installation, we need to ensure that Boost Python is linked against Homebrew version of Python and not System Python. You can check the Python error report to check if there are any references to Python system libraries.

Use the following commands (in terminal) to check that.

otool -L [Caffe installation directory]/python/caffe/_caffe.so
otool -L /usr/local/opt/boost-python/lib/libboost_python.dylib

Note: You can replace the above libboost_python.dylib path with /usr/local/Cellar/boost-python/1.57.0/lib/libboost_python.dylib as well. (Additional info: Homebrew in /usr/local/Cellar/ - every formula is also linked to a /usr/local/opt directory. It provides a path for a formula's contents that does not change across version upgrades.)

otool is a command line tool that is being used to find dependencies of an executable. ‘-L’ option searches for the shared libraries used.

As a result of the above command, you may see a reference to Python system libraries as given below.
/System/Library/Frameworks/Python.framework/Versions/2.7/Python

Then you need to change the location to Homebrew version of Python using "install_name_tool" as given below.

install_name_tool [-change old new] input

E.g.,
sudo install_name_tool -change /System/Library/Frameworks/Python.framework/Versions/2.7/Python /usr/local/Frameworks/Python.framework/Versions/2.7/Python /usr/local/opt/boost-python/lib/libboost_python.dylib


After this, try import caffe, it should work as expected.

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