what is the difference between 'import a.b as b' and 'from a import b' in python [duplicate]

Answer 1

I am going to provide only a partial answer, and I will speculate a bit.

1) Sometimes I have observed that the second way works while the first does not. On my system:

Python 3.6.3 (default, Oct  3 2017, 21:45:48) 
[GCC 7.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from tensorflow import keras   # <- this works
>>>
>>> import tensorflow.keras as K   # <- this fails
Traceback (most recent call last):
  File "", line 1, in 
ModuleNotFoundError: No module named 'tensorflow.keras'
>>> 

2) I usually don't see a difference between these two approaches to importing. I haven't investigated WHY there is a difference with TensorFlow. It may have to do with what names are imported to the top level by the various TensorFlow subfolder init.py files (which are completely empty in most cases, but the one in ../dist_packages/tensorflow/python is pretty long).