guidelines for importing modules in python

Question

I know that there have been a number of questions concerning importing modules in python, but my question seems to be somewhat different.

I'm trying to understand when you have to import a whole module as opposed to when you have to import a specific entry in the module. It seems that only one of the two ways work.

For example if I want to use basename, importing os.path doesn't do the trick.

>>> import os.path
>>> basename('scripts/cy.py')
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
NameError: name 'basename' is not defined

Instead I need to import basename from os.path as in

>>> from os.path import basename
>>> basename('scripts/cy.py')
'cy.py'

Going the other way, if I want to use shutil.copyfile, importing copyfile from shutil doesn't work

>>> 
>>> from shutil import copyfile
>>> 
>>> shutil.copyfile('emma','newemma')
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
NameError: name 'shutil' is not defined

Instead I must import shutil as in

>>> 
>>> import shutil
>>> 
>>> shutil.copyfile('emma','newemma')
'newemma'
>>> 

The only way I have been able to get this right is through experimentation. Are there some guidelines to avoid experimentation?

• Daniel: What it comes down to is: You can only reference whatever strings you've used in the import statement, thus import a.b; a.b.c() is valid and so is from a.b import c; c(), but these two are invalid: import a.b; c() (You're treating it like a global object), from a.b import c; c() (The module is 'forgotten' by Python).
• Daniel: I guess you're used to the way #include works in C. In Python, you're not copy-pasting the module. The interpreter opens it, reads it and interprets it, then creates a 'variable' pointing at the module and its contents.
• Daniel: And great, I can't edit my comment anymore, but the last sample should be from a.b import c; a.b.c().

Answer 1

If you import

import os.path

then you have to use full namespace os.path

os.path.basename()

If you import with from

from shutil import copyfile

then you don't have to use full namespace shutil

copyfile(...)

That's all.

---

If you use as

import os.path as xxx

then you have to use xxx instead of os.path

xxx.basename()

---

If you use from and as

from os.path import basename as xxx

then you have to use xxx instead of basename

xxx()

• sp________: xxx.basename()

Answer 2

you could use form module import *

from time import *
sleep(2)

which allow you to call its submodules, instead of:

from time import sleep
sleep(2)

or:

import time
time.sleep(2)

this imports every sub-module of the package https://docs.python.org/2/tutorial/modules.html#importing-from-a-package

• jwodder: Don't do this. from ... import * makes a mess of your namespace and is bad style.
• Shailyn Ortiz: this is exactly what he asked for, and even tho I shared a link to the documentation when it points out all it's side effects and if the module designer made an all it won't make a mess, so why this down-vote? :T @jwodder