python - Why does from scipy import spatial work, while scipy.spatial doesn't work after import scipy?

Question

I would like to use scipy.spatial.distance.cosine in my code. I can import the spatial submodule if I do something like import scipy.spatial or from scipy import spatial, but if I simply import scipy calling scipy.spatial.distance.cosine(...) results in the following error: AttributeError: 'module' object has no attribute 'spatial'.

What is wrong with the second approach?

Answer 1

Importing a package does not import submodule automatically. You need to import submodule explicitly.

For example, import xml does not import the submodule xml.dom

>>> import xml
>>> xml.dom
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'dom'
>>> import xml.dom
>>> xml.dom
<module 'xml.dom' from 'C:Python27libxmldom\__init__.pyc'>

There's an exception like os.path. (os module itself import the submodule into its namespace)

>>> import os
>>> os.path
<module 'ntpath' from 'C:Python27lib
tpath.pyc'>