9.2. Local and global variables

To understand local and global variables we will go through two examples.

#!/usr/bin/env python
def change(b):
    a = 90
    print a
a = 9
print "Before the function call ", a
print "inside change function",
change(a)
print "After the function call ", a

The output

$ ./local.py
Before the function call  9
inside change function 90
After the function call  9

First we are assigning 9 to a, then calling change function, inside of that we are assigning 90 to a and printing a. After the function call we are again printing the value of a. When we are writing a = 90 inside the function, it is actually creating a new variable called a, which is only available inside the function and will be destroyed after the function finished. So though the name is same for the variable a but they are different in and out side of the function.

#!/usr/bin/env python
def change(b):
    global a
    a = 90
    print a
a = 9
print "Before the function call ", a
print "inside change function",
change(a)
print "After the function call ", a

Here by using global keyword we are telling that a is globally defined, so when we are changing a's value inside the function it is actually changing for the a outside of the function also.