Python: Local and Global Variable

Local and Global Variable

•  Scope of the variable means ‒ The part of the program in which a variable is accessible.

•  Lifetime of variable means ‒ Duration for which the variable exists.

•  Definition of global variable: A variable which is defined in the main body of a file is called a global variable. It will be visible throughout the file and also inside any file which imports that file.

• Only objects which are intended to be used globally, like functions and classes, should be put in the global namespace.

•  Definition of local variable: A variable which is defined inside a function is local to that function. It is accessible from the point at which it is defined until the end of the function and exists for as long as the function is executing.

•  The parameter names in the function definition behave like local variables, but they contain the values that we pass into the function when we call it.

•  When we use the assignment operator (=) inside a function, its default behaviour is to create a new local variable.

For example 

a=10 # a is Global Variable

def My_Function(b):# b is Local variable

      c=30 # c is Local variable

      print("b = ",b)

      print("c=",c)

Output

In [14]:

My_Function (20)

print("a = ",a)#a still exists

print("b = ",,b)#being Local variable, it does not exist outside function

print("c = ",,c)#being Local variable, it does not exist outside function

b = 20

C = 30

a = 10

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                                                                   Traceback (most recent call last)

NameError

Cell In[14], line 3

        1 My_Function(20)

        2 print("a = ",a)#a still exists

‒‒‒‒> 3 print("b = ",b)#being Local variable, it does not exist outside function

        4 print("c = ",c)

NameError: name 'b' is not defined

Difference between local and global variable

Local variable

1. A variable which is declared inside a function is called as local variable.

2. Accessibility of variable is only within the function in which it is declared.

3. The local variable is created when the function(in which it is defined) starts executing and it is destroyed when the execution is complete.

4. It is preferred as local variables are more reliable. Because the values cannot be changed outside the function.

Global variable

1. A variable that is declared outside the function is called global variable.

2. Accessibility of variable is throughout the program. All functions in the program can access the global variable.

3. The global remains throughout the entire program execution.

4. It is generally not preferred as any function can change the values of global variable.