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)
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Running setup file ...
Options: {'profile': False, 'annotate': False, 'linetrace': False, 'no_cuda': False}
**************************************************
*** WARNING: nvcc not in path.
*** WARNING: Please set path to nvcc.
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Include directories: []
Library directories: []
*** WARNING: Skip installing cuda support
*** WARNING: Check your CFLAGS environment variable
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Include directories: []
Library directories: []
[Errno 1] Operation not permitted
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*** WARNING: Include files not found: ['cublas_v2.h', 'cuda.h', 'cuda_profiler_api.h', 'cuda_runtime.h', 'curand.h', 'nvToolsExt.h']
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*** 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
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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
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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
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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)