Visibility of global variables in imported modules

Question

I ve run into a bit of a wall importing modules in a Python script  I ll do my best to describe the error  why I run into it  and why I m tying this particular approach to solve my problem  which I will describe in a second    Let s suppose I have a module in which I ve defined some utility functions classes  which refer to entities defined in the namespace into which this auxiliary module will be imported  let  a  be such an entity    module1   def f        print a   And then I have the main program  where  a  is defined  into which I want to import those utilities   import module1 a 3 module1 f     Executing the program will trigger the following error   Traceback  most recent call last     File  Z  Python main py   line 10  in  lt module gt      module1 f     File  Z  Python module1 py   line 3  in f     print a NameError  global name  a  is not defined   Similar questions have been asked in the past  two days ago  d uh  and several solutions have been suggested  however I don t really think these fit my requirements  Here s my particular context   I m trying to make a Python program which connects to a MySQL database server and displays modifies data with a GUI  For cleanliness sake  I ve defined the bunch of auxiliary utility MySQL-related functions in a separate file  However they all have a common variable  which I had originally defined inside the utilities module  and which is the cursor object from MySQLdb module  I later realised that the cursor object  which is used to communicate with the db server  should be defined in the main module  so that both the main module and anything that is imported into it can access that object   End result would be something like this   utilities module py   def utility 1 args       code which references a variable named  cur  def utility n args       etcetera   And my main module   program py   import MySQLdb  Tkinter db MySQLdb connect  blahblah    cur db cursor     cur is defined  from utilities module import     And then  as soon as I try to call any of the utilities functions  it triggers the aforementioned  global name not defined  error   A particular suggestion was to have a  from program import cur  statement in the utilities file  such as this   utilities module py   from program import cur  rest of function definitions   program py   import Tkinter  MySQLdb db MySQLdb connect  blahblah    cur db cursor     cur is defined  from utilities module import     But that s cyclic import or something like that and  bottom line  it crashes too  So my question is   How in hell can I make the  cur  object  defined in the main module  visible to those auxiliary functions which are imported into it   Thanks for your time and my deepest apologies if the solution has been posted elsewhere  I just can t find the answer myself and I ve got no more tricks in my book

User · Answer

The easiest solution to this particular problem would have been to add another function within the module that would have stored the cursor in a variable global to the module. Then all the other functions could use it as well.

module1:

cursor = None

def setCursor(cur):
    global cursor
    cursor = cur

def method(some, args):
    global cursor
    do_stuff(cursor, some, args)

main program:

import module1

cursor = get_a_cursor()
module1.setCursor(cursor)
module1.method()

User · Answer

The OOP way of doing this would be to make your module a class instead of a set of unbound methods  Then you could use   init   or a setter method to set the variables from the caller for use in the module methods

User · Answer

Since I haven t seen it in the answers above  I thought I would add my simple workaround  which is just to add a global dict argument to the function requiring the calling module s globals  and then pass the dict into the function when calling  e g     external module def imported function global dict None       print global dict  a        calling module a   12 from external module import imported function imported function global dict globals      gt  gt  gt  12

User · Answer

This post is just an observation for Python behaviour I encountered  Maybe the advices you read above don t work for you if you made the same thing I did below   Namely  I have a module which contains global shared variables  as suggested above     sharedstuff py  globaltimes randomnode    globalist randomnode      Then I had the main module which imports the shared stuff with   import sharedstuff as shared   and some other modules that actually populated these arrays  These are called by the main module  When exiting these other modules I can clearly see that the arrays are populated  But when reading them back in the main module  they were empty  This was rather strange for me  well  I am new to Python   However  when I change the way I import the sharedstuff py in the main module to   from globals import     it worked  the arrays were populated    Just sayin

User · Answer

Globals in Python are global to a module  not across all modules   Many people are confused by this  because in  say  C  a global is the same across all implementation files unless you explicitly make it static    There are different ways to solve this  depending on your actual use case     Before even going down this path  ask yourself whether this really needs to be global  Maybe you really want a class  with f as an instance method  rather than just a free function  Then you could do something like this   import module1 thingy1   module1 Thingy a 3  thingy1 f       If you really do want a global  but it s just there to be used by module1  set it in that module   import module1 module1 a 3 module1 f       On the other hand  if a is shared by a whole lot of modules  put it somewhere else  and have everyone import it   import shared stuff import module1 shared stuff a   3 module1 f         and  in module1 py   import shared stuff def f        print shared stuff a   Don t use a from import unless the variable is intended to be a constant  from shared stuff import a would create a new a variable initialized to whatever shared stuff a referred to at the time of the import  and this new a variable would not be affected by assignments to shared stuff a     Or  in the rare case that you really do need it to be truly global everywhere  like a builtin  add it to the builtin module  The exact details differ between Python 2 x and 3 x  In 3 x  it works like this   import builtins import module1 builtins a   3 module1 f

User · Answer

Since globals are module specific  you can add the following function to all imported modules  and then use it to   Add singular variables  in dictionary format  as globals for those Transfer your main module globals to it     addglobals   lambda x  globals   update x   Then all you need to pass on current globals is   import module module addglobals globals

User · Answer

As a workaround  you could consider setting environment variables in the outer layer  like this     main py   import os os environ  MYVAL     str myintvariable    mymodule py   import os  myval   None if  MYVAL  in os environ      myval   os environ  MYVAL     As an extra precaution  handle the case when MYVAL is not defined inside the module

User · Answer

A function uses the globals of the module it s defined in  Instead of setting a   3  for example  you should be setting module1 a   3  So  if you want cur available as a global in utilities module  set utilities module cur   A better solution  don t use globals  Pass the variables you need into the functions that need it  or create a class to bundle all the data together  and pass it when initializing the instance

[python] Visibility of global variables in imported modules

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