Communication between two Python files

Question

I'm having a problem with importing files which can be simplified as this:

a.py:

import b

a = 0
b.foo()

b.py:

import a

def foo():
    a.a=4

So, what I'm trying to do is: in file a.py call the function foo() from b.py which would then change the value of a variable that is in a.py. This is the error I get:

AttributeError: module 'b' has no attribute 'foo'

What am I doing wrong? What would be the proper way to do this?

yes. Import either of them to one. This will fix your problem. — Ria Sen, Apr 21 '17 at 06:35
its loop. you running `a.py` and `a.py` import `b.py` and `b.py` import 'a.py', so it is not good programming to create this type of loop in code. — Vivek Sable, Apr 21 '17 at 06:36
They are in the same location. Importing just one of them doesn't work, the method in b.py just creates a new variable 'a' in it's scope. — Njubster, Apr 21 '17 at 06:42

hiro protagonist · Answer 1 · 2017-04-21T06:54:07.690

2

your import is circular. you need to come up with a way of testing that with a non-circular import. e.g. create a new main file that you execute; import a.a and b.foo there:

main.py

from b import foo
import a

a.a = 7
foo()

a.py

a = 0

b.py

import a

def foo():
    a.a=4

edited Apr 21 '17 at 06:54

answered Apr 21 '17 at 06:42

hiro protagonist

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But how do I address the variable 'a' in b.py then? – Njubster Apr 21 '17 at 06:43
@Njubster added an example. – hiro protagonist Apr 21 '17 at 06:55
So, does that mean that the thing that I'm asking for is not doable without the third file? – Njubster Apr 21 '17 at 06:55
what is not doable is to import a from b and b from a at the same time. that is what is called a circular import. – hiro protagonist Apr 21 '17 at 06:57
Ok, thanks man, I guess I'll try to avoid doing the circular thingie. – Njubster Apr 21 '17 at 07:11

score 1 · Answer 2 · answered Apr 21 '17 at 07:03

1

First and foremost thing is making circular import, and fixing it is not a good idea.

But try to do small change in your code and solve.

a.py:

from b import foo

a = 0
foo()
print a

b.py:

def foo():
    import a as filea
    filea.a=4

when you run a.py, watch the print a, it is executing two times. You need to be at your own risk by fixing lot of such things. Instead of doing all circus, better to avoid circular import.

answered Apr 21 '17 at 07:03

Hara

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I'm curious, what's the risk? – Njubster Apr 21 '17 at 07:10
all your globals `a.py` will be called multiple times is one point. – Hara Apr 21 '17 at 07:12
@Njubster You can try to use `pycharm`, and debug step by step, and see the flow, you will get to know more clear, what is happening, with this two files code. – Hara Apr 21 '17 at 07:21

Communication between two Python files

2 Answers2