Import vs from

Import X :

• imports the module X, and creates a reference to that module in the current namespace. Then you need to define completed module path to access a particular attribute or method from inside the module. 
• For example: X.name or X.attribute

From X import * :

• * imports the module X, and creates references to all public objects defined by that module in the current namespace (that is, everything that doesn’t have a name starting with “_”) or what ever the name you mentioned. Or in other words, after you’ve run this statement, you can simply use a plain name to refer to things defined in module X. But X itself is not defined, so X.name doesn’t work. And if name was already defined, it is replaced by the new version. And if name in X is changed to point to some other object, your module won’t notice.* This makes all names from the module available in the local namespace.

Now let’s see when we do import X.Y:

>>> import sys

>>> import os.path

Check sys.modules with name os and os.path:

>>> sys.modules['os']

<module 'os' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.pyc'>

>>> sys.modules['os.path']

<module 'posixpath' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

Check globals() and locals() namespace dict with name os and os.path:

 >>> globals()['os']

<module 'os' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.pyc'>

>>> locals()['os']

<module 'os' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.pyc'>

>>> globals()['os.path']

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

KeyError: 'os.path'

>>>

From the above example we found that only os is inserted in the local and global namespace. So, we should be able to use:

>>> os

 <module 'os' from

  '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.pyc'>

 >>> os.path

 <module 'posixpath' from

 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

 >>>

But not path

>>> path

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

NameError: name 'path' is not defined

>>>

Once you delete the os from locals() namespace, you won't be able to access os as well as os.path even though they exist in sys.modules:

>>> del locals()['os']

>>> os

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

NameError: name 'os' is not defined

>>> os.path

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

NameError: name 'os' is not defined

>>>

Now let's come to from :

** from :**

>>> import sys

>>> from os import path

Check sys.modules with name os and os.path:

>>> sys.modules['os']

<module 'os' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.pyc'>

>>> sys.modules['os.path']

<module 'posixpath' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

Oh, we found that in sys.modules we found as same as we did before by using import name

OK, let's check how it looks like in locals() and globals() namespace dict:

>>> globals()['path']

<module 'posixpath' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

>>> locals()['path']

<module 'posixpath' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

>>> globals()['os']

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

KeyError: 'os'

>>>

You can access by using name path not by os.path:

>>> path

<module 'posixpath' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

>>> os.path

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

NameError: name 'os' is not defined

>>>

Let's delete 'path' from locals():

>>> del locals()['path']

>>> path

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

NameError: name 'path' is not defined

>>>

One final example using an alias:

>>> from os import path as HELL_BOY

>>> locals()['HELL_BOY']

<module 'posixpath' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

>>> globals()['HELL_BOY']

<module 'posixpath' from /System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.pyc'>

And no path defined:

>>> globals()['path']

Traceback (most recent call last):

 File "<stdin>", line 1, in <module>

KeyError: 'path'

>>>

https://stackoverflow.com/a/21547583