python import within import

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.

Circular imports can lead to annoying problems, so it would be better to avoid this kind of import pattern. If both first and second need access to some_var, you could create third module and put some_var in there. — Heikki Toivonen
– Heikki Toivonen, Commented Nov 16, 2013 at 0:36

John La Rooy · Accepted Answer · 2013-11-16 00:18:47Z

3

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

answered Nov 16, 2013 at 0:18

John La Rooy

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1 Comment

mulllhausen Over a year ago

thanks for explaining why the wildcard is discouraged

Andrew Clark · Accepted Answer · 2013-11-16 00:19:47Z

1

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.

answered Nov 16, 2013 at 0:19

Andrew Clark

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Comments

user2884344 · Accepted Answer · 2013-11-16 01:37:57Z

0

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?

answered Nov 16, 2013 at 1:37

user2884344

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1 Comment

mulllhausen Over a year ago

basically i have common library files which i use in a lot of projects (many files with the role of 'second' in this example) and then i have higher level library files per project (ie many files with the role of 'first' in this example). so each project only needs to know about 'first', and 'first' only needs to know about 'second'. i know a class structure with first extends second would be ideal, but i'm just trying to see if i can use modules and avoid classes...

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