Global variables

Posted by Poromenos on Mon 05 May 2003 06:09 PM — 13 posts, 84,766 views.

Poromenos Greece Mon 05 May 2003 06:09 PM #0

Is there any way I can set global variables that I can change, in Python? I hate it that they disappear every time my function exits :/

Ixokai USA Tue 06 May 2003 03:34 AM #1

You just have to set them outside of the function... For example, if you do 'Send to Script', I notice that the command that is entered int he send area is interpreted as script-code.. I think it might be executed in the global scope, before any script function is called... YOu can access any variables there in the function, but they may be global and therefore remain... Test it out.

I /do/ know that this works:

/somevar = "Er, hi!"
/world.note(somevar)

So 'somevar' is indeed being set in the global scope...

Nick Gammon Australia Forum Administrator Tue 06 May 2003 05:35 AM #2

My tests also indicate that a script function which sets a variable of global scope will set a variable which persists until next time (eg. an alias that sets a variable in a script, and another that tests it).

I am talking Python variables here, not MUSHclient variables.

HOWEVER, there was a problem with syntax errors. I discovered that when Python gave a syntax error it marked the script engine as "disconnected", and that further attempts to script silently failed.

Thus I recently changed it (for Python's benefit really) that if the script engine was in a disconnected state when you went to execute a script it reconnected it. This probably means it reinitialises variables.

However the exact same logic is there for the other script engines.

Thus what will happen, and is probably happening to you, is:

1. You set a variable: /a = 42
2. You make a typing error, and get syntax error
3. You get it right, but the variable has gone: /world.note (a)

Basically this is a development problem. It should go away once the scripts are debugged.

Nick Gammon Australia Forum Administrator Tue 06 May 2003 08:11 AM #3

Quote:

For example, if you do 'Send to Script', I notice that the command that is entered in the send area is interpreted as script-code.. I think it might be executed in the global scope

Yes, that is what it is intended to do, and yes, it executes in global scope.

Poromenos Greece Tue 06 May 2003 08:11 PM #4

intSomeInt = 3

def MyFunc:
intSomeInt = 2

Boom, error...
The secret is:

def MyFunc:
global intSomeInt
intSomeInt = 2

Nick Gammon Australia Forum Administrator Tue 06 May 2003 09:18 PM #5

Ah, strangely, PHP behaves the same way, as I should know, as I do these web pages in it.

Any references to variables in a subroutine are assumed local unless it is told otherwise. I didn't know enough about Python to know that, and my tests were of variables in global scope.

Ixokai USA Fri 09 May 2003 11:11 PM #6

Not *pecisely*. In Python you only need the "global" if you are going to assign to the global variable... to read from it, it traverses the scope-hierarchy and discovers the global all by itself..

Poromenos Greece Sat 10 May 2003 02:35 AM #7

Quote:
Is there any way I can set global variables that I can change, in Python?

Nick Gammon Australia Forum Administrator Sat 10 May 2003 04:22 AM #8

In what way is your question not answered? Can you give an example?

Ixokai USA Sat 10 May 2003 08:25 AM #9

Nick, I can't seem to reproduce the behavior you described, with the script engine being 'disconnected' on a syntax error...

I mean...
[code]/a = 42
/if blah there
(gives syntax error)
/world.note(a)
(gives 42)
[/code]

What are you doing that produces the disconnection?

Poromenos Greece Sat 10 May 2003 01:09 PM #10

Quote:

In what way is your question not answered? Can you give an example?

No, it's answered, i was referring to ixokai :)

Nick Gammon Australia Forum Administrator Sat 10 May 2003 09:36 PM #11

Re the disconnection, I am glad the variable is preserved, I was guessing that it did not, and thought that might be Poremenos' problem. In my post I said "This probably means it reinitialises variables.".

Seems it is smarter than that, and my word "probably" was covering the fact that I hadn't actually tested it. :)

First Lensman Tue 03 Feb 2009 01:05 PM #12

It was recommended in a python manual to create a class 
that holds global variables. Here is an example that I 
culled from a script I wrote to work with the mailman 
software package:

class GlobalVariables:
    'Class that holds Global Variables'
    def __init__(self):
        self.LDIR = '/var/lib/mailman/lists'
        self.BDIR = '/usr/lib/mailman/bin'
        self.THLD = ''
        self.MLST = ''
        self.EOJ = 0


Then, in the main(), create a varaible using this class:

def main():
    global GL
    GL = GlobalVariables()
    input_list()
    process_list()


In any other subroutine that would need access to the 
Global Variables, just include the global statement. The 
following code is a very simplified version from my script:

def input_list():
    global GL
    GL.MLST = raw_input("Enter Mailing List: ")

def process_list():
    global GL
    cfgfile = '/tmp/'+GL.MLST+'_config'
    regfile = '/tmp/'+GL.MLST+'_member'
    digfile = '/tmp/'+GL.MLST+'_digest'


As you can see, it is much easier to remember the "global GL" 
in each routine rather than multiple "global" statements!