Global variable declaration

[psbasha]

Hi,

Global variables are declared before the class definition and after the modules of the application declaration.

Please correct me if I am wrong.

Thanks
PSB

[psbasha]

I have a global variable declared in the Module.I have to make use of this global variable in another class/ class method.

Could anybody help me by explainning the sample code.

Thanks in advance
PSB

[ghostdog74]

I have a global variable declared in the Module.I have to make use of this global variable in another class/ class method.

Could anybody help me by explainning the sample code.

Thanks in advance
PSB

to use global variable from another class/method/function, just include the "global" keyword in that class/method/function.

[bartonc]

I have a global variable declared in the Module.I have to make use of this global variable in another class/ class method.

Could anybody help me by explainning the sample code.

Thanks in advance
PSB

While I highly recommend AGAINST gobals, mutable types will pass between modules:

#test.py
# module holds globals
globalList = []
globalInt = 5

def printGlobals():
    print globalList
    print globalInt


class GlobalModifier:
    def ModifyGlobals(self):
        global globalList
        global globalInt

        globalList.append("hello")
        globalInt = 7

# module1.py
# module1 uses golbal from test.py
import test
from test import globalList, globalInt
globalList.append(0)
test.printGlobals()

gm = test.GlobalModifier()
gm.ModifyGlobals()

print globalList, globalInt
test.printGlobals()

but not immutable types:
[0]
5
[0, 'hello'] 5
[0, 'hello']
7

[bvdet]

I have a global variable declared in the Module.I have to make use of this global variable in another class/ class method.

Could anybody help me by explainning the sample code.

Thanks in advance
PSB

The global namespace for a function or variable is always the module in which it was defined. To access the global variable from another module:

import yourModule
localVariable = yourModule.globalVariable

[bartonc]

While I highly recommend AGAINST gobals, mutable types will pass between modules:

#test.py
# module holds globals
globalList = []
globalInt = 5

def printGlobals():
    print globalList
    print globalInt


class GlobalModifier:
    def ModifyGlobals(self):
        global globalList
        global globalInt

        globalList.append("hello")
        globalInt = 7

# module1.py
# module1 uses golbal from test.py
import test
from test import globalList, globalInt
globalList.append(0)
test.printGlobals()

gm = test.GlobalModifier()
gm.ModifyGlobals()

print globalList, globalInt
test.printGlobals()

but not immutable types:
[0]
5
[0, 'hello'] 5
[0, 'hello']
7

The very good reason for this is that program errors are very hard to track down when more than one module is allowed to modify a variable.

[bartonc]

The very good reason for this is that program errors are very hard to track down when more than one module is allowed to modify a variable.

The mutable type to use between modules would be a class:

# test.py
# class holds globals

import inspect # just for testing this idea

def PrintGlobRep():
    for member in inspect.getmembers(globRep):
        if not member[0].startswith('_'):
            print member

class GlobalRepository:
    globalList = []
    globalInt = 5


globRep = GlobalRepository()

# module1.py

# module1 uses Global Repository from test.py

import test # this does initialization of the Global Repository
from test import globRep # get the class instance

test.PrintGlobRep()
globRep.newGlobal = 12
test.PrintGlobRep()

('globalInt', 5)
('globalList', [])
('globalInt', 5)
('globalList', [])
('newGlobal', 12)

[psbasha]

Sample.py
iVar =1

class Sample1:

    def Func1(self):
        global iVar
        iVAr = 20
        
        print iVAr
    
    def Func2(self):
        pass

class Sample2:

    def Func3(self):
        pass
    
    def Func4(self):
        global iVar
        print iVar
             
        print iVar
        

if __name__ == '__main__':
    
    obj1 = Sample1()
    obj2 = Sample2()

    obj1.Func1()
    obj2.Func4()
    print iVar

>>>
20
1
1
1
>>>

But I was expecting the output will be

>>>
20
20
20
20
>>>

Can anybody help me in understanding the output.

Thnaks
PSB

[bartonc]

The mutable type to use between modules would be a class:

# test.py
# class holds globals

import inspect # just for testing this idea

def PrintGlobRep():
    for member in inspect.getmembers(globRep):
        if not member[0].startswith('_'):
            print member

class GlobalRepository:
    globalList = []
    globalInt = 5


globRep = GlobalRepository()

# module1.py

# module1 uses Global Repository from test.py

import test # this does initialization of the Global Repository
from test import globRep # get the class instance

test.PrintGlobRep()
globRep.newGlobal = 12
test.PrintGlobRep()

('globalInt', 5)
('globalList', [])
('globalInt', 5)
('globalList', [])
('newGlobal', 12)

Class instances can have "global" data by using class variables:

# class with shared variables

class WithSharedVariables:
    ## class variables
    globalList = []
    globalInt = 5

    def __init__(self):
        self.localInt = 11

    def printClassVars(self):
        print WithSharedVariables.globalList
        print WithSharedVariables.globalInt

    def IncGlobalInt(self):
        WithSharedVariables.globalInt += 1

    def AppendGlobalList(self, item):
        WithSharedVariables.globalList.append(item)



wsv1 = WithSharedVariables()
wsv2 = WithSharedVariables()

wsv2.IncGlobalInt()
wsv1.AppendGlobalList("hello")

wsv2.printClassVars()

[bartonc]

Sample.py
iVar =1

class Sample1:

    def Func1(self):
        global iVar
        iVAr = 20
        
        print iVAr
    
    def Func2(self):
        pass

class Sample2:

    def Func3(self):
        pass
    
    def Func4(self):
        global iVar
        print iVar
             
        print iVar
        

if __name__ == '__main__':
    
    obj1 = Sample1()
    obj2 = Sample2()

    obj1.Func1()
    obj2.Func4()
    print iVar

>>>
20
1
1
1
>>>

But I was expecting the output will be

>>>
20
20
20
20
>>>

Can anybody help me in understanding the output.

Thnaks
PSB

You've got a typo:

iVar =1

class Sample1:

    def Func1(self):
        global iVar
        iVAr = 20

[psbasha]

Is the above sample piece of code for Global variable access is correct?.If not how to change the global variable value from '1' to '20' value.


-PSB

[bartonc]

Sample.py
iVar =1

class Sample1:

    def Func1(self):
        global iVar
        iVAr = 20
        
        print iVAr
    
    def Func2(self):
        pass

class Sample2:

    def Func3(self):
        pass
    
    def Func4(self):
        global iVar
        print iVar
             
        print iVar
        

if __name__ == '__main__':
    
    obj1 = Sample1()
    obj2 = Sample2()

    obj1.Func1()
    obj2.Func4()
    print iVar

>>>
20
1
1
1
>>>

But I was expecting the output will be

>>>
20
20
20
20
>>>

Can anybody help me in understanding the output.

Thnaks
PSB

The error is here:
iVAr = 20
should be
iVar = 20
That will fix it.

[psbasha]

Thanks barton

Sorry, for me not noticing the correction of the bug.

Now I understood the concept of Global.I was familar with C++ global variables,then I thought the same concept should apply for any other programming language.

The concept is same "globally" :)

-PSB

[bartonc]

Thanks barton

Sorry, for me not noticing the correction of the bug.

Now I understood the concept of Global.I was familar with C++ global variables,then I thought the same concept should apply for any other programming language.

The concept is same "globally" :)

-PSB

That's really no problem.
So, what part of the globe are you located in, anyway?

[psbasha]

Sample1.py
class CSample1:

    def Func1(self):
        global iVar
        iVar = 20
        
        print iVar
    
    def Func2(self):
        pass

Sample2.py

class CSample2:

    def Func3(self):
        pass
    
    def Func4(self):
        global iVar
        print iVar

Main.py

from Sample1 import CSample1
from Sample2 import CSample2

if __name__ == '__main__':
  
    
    obj1 = CSample1()
    obj2 = CSample2()

    obj1.Func1()
    obj2.Func4()
    print iVar

I am getting the following error

Traceback (most recent call last):
File "C:\Python24\Li b\site-packages\python win\pywin\frame work\scriptutil s.py", line 307, in RunScript
debugger.run(co deObject, __main__.__dict __, start_stepping= 0)
File "C:\Python24\Li b\site-packages\python win\pywin\debug ger\__init__.py ", line 60, in run
_GetCurrentDebu gger().run(cmd, globals,locals, start_stepping)
File "C:\Python24\Li b\site-packages\python win\pywin\debug ger\debugger.py ", line 631, in run
exec cmd in globals, locals
File "[EDITED OUT]", line 11, in ?
obj2.Func4()
File "[EDITED OUT]", line 9, in Func4
print iVar
NameError: global name 'iVar' is not defined
>>>