导入中的python导入

Question

i am trying to import a module within a module and then access the lower level module from the top, however it is not available. is this normal behaviour?

# caller.py
import first
print second.some_var

# first.py
import second

# second.py
some_var = 1

running caller.py gives error

NameError: name 'second' is not defined

do i have to import second within caller.py ? this seems counter-intuitive to me.

Answer 1

You can use

import first
print first.second.some_var

Having second appear in the namespace automatically just by importing first would lead to lots of conflicts

This would also work

from first import second
print second.some_var

The use of wildcard

from first import *

is discouraged because if someone adds extra attributes/functions to first they may overwrite attributes you are using locally if they happen to choose the same name

Answer 2

import first will import the name first into the global namespace, but it does not import everything from first into the namespace. So you can do one of the following:

• Access second through first :

   import first print first.second.some_var 

• Import second directly into the namespace of caller.py:

   from first import second print second.some_var 

Note that you can use from first import * to import all of the names from first into the namespace, but this is generally discouraged.

Answer 3

instead use:

from first import second
print first.second.some_var

It is a lot more compressed too. Why are you doing your way anyway?