12 STD - CH: 3 : LEGB rule

 LEGB rule

Scope also defines the order in which variables have to be mapped to the object in order to obtain the value. Let us take a simple example as shown below:
1. x:= 'outer x variable'
2. display():
3. x:= 'inner x variable'
4. print x
5. display()
When the above statements are executed the

statement (4) and (5) display the result as Output outer x variable
inner x variable Above statements give different outputs because the same variable name x resides in different scopes, one inside the
function display() and the other in the upper level. The value ‘outer xvariable’ is printed when x is referenced outside the function
definition. Whereas when display() gets executed, ‘inner x variable’ is printed which  is the x value inside the function definition. From the above example, we can guess that there is a rule followed, in order to decide from which scope a variable has to be picked. 

The LEGB rule is used to decide the order in which the scopes are to be searched for scope resolution. The scopes are listed below in terms of hierarchy (highest to lowest).

 

 

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