from google.colab import output
#I don't know why nbextensions don't work with python3.6 
with output.temporary():
  !pip install --upgrade git+https://github.com/Kreijstal/colab_inspector.git 
  !python2.7 -m pip install --upgrade git+https://github.com/blois/colab_inspector.git #yes, really.
  !jupyter nbextension install --py inspector

import inspector

# open a scratch cell (Ctrl+Alt+N)
# run there
# inspector.watch_globals()