Static variables in Python that are shared across files

Question

I am pretty new to Python and I could't find a way to have static variables that are shared across different python files... In Java, it seems quite straight forward to do so... Here is what I'm trying to do:

data.py

class Shared(object):
    list_vars = []
    var = ""

    @staticmethod
    def print_vars():
        print "list_vars = " + str(Shared.list_vars)
        print "var = " + Shared.var

user1.py

import time
from data import Shared

Shared.list_vars.append("001")
time.sleep(5.0)
Shared.print_vars()

# It prints:
# list_vars = ['001']
# var =

user2.py

import time
from data import Shared

Shared.var = "002"
time.sleep(5.0)
Shared.print_vars()

# It prints:
# list_vars = []
# var = 002

Sorry, this may not be the best example but it catches the idea... my question is, if I want to have:

list_vars = ['001']
var = 002

in one of the/even some other python files or classes after running both user1.py and user2.py (I am considering user1.py and user2.py as two sub-programs in the same software package that are normally being run at the same time), what is the "Python way" to do so?

Thanks a lot!

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Updates for the question:

To be a little more specific to the problem, please allow me to describe the problem in this way:

data.py

class Shared(object):
    list_vars = []
    var = ""

    @staticmethod
    def print_vars():
        print "list_vars = " + str(Shared.list_vars)
        print "var = " + Shared.var

    # Can be considered as a separate thread running in the background, waiting for messages
    @staticmethod
    def callback(message):
        if message.event == "add":
            Shared.list_vars.append(message.data)
        elif message.event == "remove" and message.data in Shared.list_vars:
            Shared.list_vars.remove(message.data)

There are two extra files, user1.py and user2.py , their content can be ignored for the moment...

So let's say user1.py and user2.py are being run at about the same time, say time = 0.

• At time = 1, there is a message comes in (with message.event = "add" and message.data = "001"), the callback function in data.py is triggered and the "001" is added to the variable list_vars .

• At time = 2, user1.py updates the variable var in data.py to "002" .

• At time = 3, if user2.py wants to access and print out the variables list_vars and var , with the latest values:

  • list_vars = ["001"]
  • var = 002

How can this be achieved in Python?

Thank you very much!

Answer 1

The problem is that (I suppose) you are launching separately user1.py and user2.py . So static values of class Shared are not preserved across different invocations.

But that's otherwise a perfectly correct way of sharing data : you declare classes or even variable in one file that is imported in the others.

But Python is not Java, and everything does not need to be a class. You could do :

• data.py

   list_vars = [] var = "" def print_vars(): print "list_vars = " + str(Shared.list_vars) print "var = " + Shared.var 

• user1.py

   import time import data as shared shared.list_vars.append("001") time.sleep(5.0) shared.print_vars() # It prints: # list_vars = ['001'] # var = 

• user2.py

   import time import data as shared shared.var = "002" time.sleep(5.0) shared.print_vars() # It prints: # list_vars = [] # var = 002 

• main.py

   import user1 # It prints: # list_vars = ['001'] # var = import user2 # It prints: # list_vars = ['001'] # var = 002