Python Global Variable Through Import?

Question

Is this form of global variable declaration good practice in Python? My dictionary has no data in B.py in some cases. Just seems inconsistent.

classes.py

class Aclass:
    dict = {}

myClass = Aclass()

A.py:

from classes import myClass

myClass.dict["variable"]

B.py:

from classes import myClass

print str(myClass.dict)

A.py is processed before B.py. This prints an empty dict {} for me.

This is a simplified question from previous post: Shared/Global Dictionary in Django Between URLs and Context Processor. Your insight is appreciated.

A.py does not do anything with the variables. It merely tries to access an entry in a dictionary. Did you mean to say myClass.dict["variable"] = "value" (or something to that effect)? — HardlyKnowEm
– HardlyKnowEm, Commented Jan 25, 2012 at 22:22
Wanted you all to know that the issue was slightly more insidious, and thank you for your help. It was importing the same files through two paths: one imported project.classes.myClass while the other imported just classes.myClass, creating two separate instances. The post that this was reduced from is this one: Shared/Global Dictionary in Django Between URLs and Context Processor — garromark
– garromark, Commented Jan 25, 2012 at 22:45

Johan Lundberg · Accepted Answer · 2012-01-26 07:45:38Z

2

if in A.py you change it to

myClass.dict["variable"]="hello"

(as pointed out in comments)

then the question becomes interesting.

it's ok but it's better to have another interface (functions, methods) to that data. It's a way to store a state of the module. The object you called myClass (!) is the same both from a and b.

multiple imports are safe and do nothing except to return the same loaded module.

edited Jan 26, 2012 at 7:45

answered Jan 25, 2012 at 22:44

Johan Lundberg

27.3k13 gold badges76 silver badges101 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Niklas R Over a year ago

... because modules that were imported before (being in the same process, o.c.) are saved in the sys.modules dictionary. :)

Collectives™ on Stack Overflow

Python Global Variable Through Import?

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related