Looks like a no to me,

[~/Documents]$ pip install chainer Querying PyPI ... Downloading package ... Opening: https://pypi.python.org/packages/29/d2/97274ffb6903a27897762043914046009000c7c78c1fe8440872f5655ce8/chainer-1.20.0.1.tar.gz Save as: /private/var/mobile/Containers/Data/Application/45AEBBCE-4FC5-44B4-9B3A-6C401C673011/tmp/chainer-1.20.0.1.tar.gz (1247648 bytes) 1247648 [100.00%] Extracting archive file ... Archive extracted. Running setup file ... Options: {'profile': False, 'annotate': False, 'linetrace': False, 'no_cuda': False} ************************************************** *** WARNING: nvcc not in path. *** WARNING: Please set path to nvcc. ************************************************** Include directories: [] Library directories: [] *** WARNING: Skip installing cuda support *** WARNING: Check your CFLAGS environment variable ************************************************** Include directories: [] Library directories: [] [Errno 1] Operation not permitted ************************************************** *** WARNING: Include files not found: ['cublas_v2.h', 'cuda.h', 'cuda_profiler_api.h', 'cuda_runtime.h', 'curand.h', 'nvToolsExt.h'] ************************************************** *** WARNING: Include files not found: ['cudnn.h'] *** WARNING: Skip installing cudnn support *** WARNING: Check your CFLAGS environment variable ************************************************** WARNING: Extension modules and skipped: [] Package installed: chainer Installing dependency: filelock Querying PyPI ... Downloading package ... Opening: https://pypi.python.org/packages/48/f0/77ece9df4df7924ad0d9ba678c8602dd1114348e1c714e4cd10d9fc35ff0/filelock-2.0.7.tar.gzSave as: /private/var/mobile/Containers/Data/Application/45AEBBCE-4FC5-44B4-9B3A-6C401C673011/tmp/filelock-2.0.7.tar.gz (4981 bytes) 4981 [100.00%] Extracting archive file ... Archive extracted. Running setup file ... Package installed: filelock Installing dependency: nose Querying PyPI ... Downloading package ... Opening: https://pypi.python.org/packages/58/a5/0dc93c3ec33f4e281849523a5a913fa1eea9a3068acfa754d44d88107a44/nose-1.3.7.tar.gz Save as: /private/var/mobile/Containers/Data/Application/45AEBBCE-4FC5-44B4-9B3A-6C401C673011/tmp/nose-1.3.7.tar.gz (280488 bytes) 280488 [100.00%] Extracting archive file ... Archive extracted. Running setup file ... Package installed: nose Dependency available in Pythonista bundle : numpy Installing dependency: protobuf Querying PyPI ... Downloading package ... Opening: https://pypi.python.org/packages/e0/2f/690a5f047e2cfef40c9c5eec0877b496dc1f5a0625ca6b0ac1cd11f12f6a/protobuf-3.2.0.tar.gz Save as: /private/var/mobile/Containers/Data/Application/45AEBBCE-4FC5-44B4-9B3A-6C401C673011/tmp/protobuf-3.2.0.tar.gz (132939 bytes) 132939 [100.00%] Extracting archive file ... Archive extracted. Running setup file ... WARNING: Extension modules and skipped: [] Package installed: protobuf Dependency available in Pythonista bundle : six Dependency available in Pythonista bundle : six [~/Documents]$

http://docs.chainer.org/en/stable/install.html mention quite a bit of c++, so definately not 100% pure python (Cython, maybe)