root@2f057d814783:/# python -c"from image_intensities import png_intensities; print(png_intensities('/image_intensities_minimal_test/tests/d94ymc6-7401014c-59fb-4a52-b314-8eed8172d33e.png'))"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python3.6/site-packages/image_intensities_test-0.0.10.dev3-py3.6-linux-x86_64.egg/image_intensities/intensities.py", line 32, in png_intensities
    result_struct = __ffi.png_intensities(filename)
AttributeError: '_cffi_backend.FFI' object has no attribute 'png_intensities'