Python global scopes

The Python global scopes has a larger scope of influence than the local scopes or enclosing scopes. The global scopes contain the global variables. Any variables declared outside the local scopes and enclosed scopes are the global variables.

Link : Python local scopes

In the global scopes the usual scoping rules still apply. This means the local variable has the most power over the local region followed by the enclosed scope variables and then the global variables.

Link : Python enclosing scopes

Consider the code example.

>>> gb=100 #A global variable
>>> def func():
	m=23 #local variable
	print('m=',m )

>>> func()
m= 23
gb= 100
>>> print( m )
Traceback (most recent call last):
  File "<pyshell#8>", line 1, in <module>
    print( m )
NameError: name 'm' is not defined

We can access the global variable ‘gb’ inside the local scope because global scope has influence over the local scope, but we cannot access the local variable ‘m’ outside the local scope. Trying to access it will give an error message as shown above.

Here is another example which shows that the local variable has more power over the global variable.

>>> hi=1111
>>> def func():
	hi=444 #Local variable
	print( 'hi=', hi )

>>> func()
hi= 444
>>> print('Outside func() hi=',hi)
Outside func() hi= 1111

Inside the local scope the local variable ‘hi'(444) is preferred over the global value. Outside the local scope the global value is preferred since the local variable has ceased to exist.

More examples

Let us test the power of global variable with the enclosed variable.

>>> k=888
>>> def Outer():
	def Inner(): #inner scope begins here
		print( 'Inner() h=',h )
		print('Inner() k=',k)
	print( 'Outer() k=',k )

>>> Outer()
Inner() h= 555
Inner() k= 89
Outer() k= 89
>>> print('k=',k)
k= 888

Inside the Inner() scope the local ‘h'(555) is preferred. In case of ‘k’, the enclosed ‘k'(89) is preferred not the global ‘k'(888).

Inside Outer() the enclosed ‘K'(89) is still preferred, not the global ‘k'(888).

Outside the enclosed scope the global variable ‘k'(888) is taken.

Changing the global object value inside the local scope

We can access the global object inside the local scope without any problem, but to change the global object value inside the local scope we must re-declare the object with the statement ‘global‘ inside the local scope. Without the re-declaration of the object, changing the value of the object is not possible.

If you create another object with the same as the global object name inside the local scope, that object is different from the global object. So the global object value remains unchanged.

consider the code below.

>>> gb=980 #global object
>>> def func():
...  gb=90 
...  print(gb) #Prints local object gb
>>> func() 
>>> gb #Gives global object value

In the code above the local scope ‘gb’ is different from the global scope ‘gb’.

To change the global object inside the local scope use the ‘global’ statement. Look a the code below.

>>> gl=123
>>> def func():
global gl

>>> func()
gl= 900
>>> gl #accessing the global object

Now the value of gl is changed to whatever it is assigned inside the function func().

Link : Python global statement

***Side note

Always remember,the order followed by Python while looking for names in a scope or namespace is : local scope> enclosing scope > global scope > built-in scope. This order is also known as ‘LEGB‘.

Link :Python scopes types