Updating Variables

A common pattern in assignment statements is an assignments statement that updates a variable – where the new value of the variable depends on the old.

>>> x = x + 1
Traceback (most recent call last):
  File "", line 1, in 
NameError: name 'x' is not defined

Unfortunately the variable x is not defined so we got an error. The x = x +1 means get the current value of x, add one, and then update x with the new value. In order to successfully update variable x let’s enter the starting value.

>>>value = raw_input(‘Enter a value:’)
Enter a value: 5
>>>x = int(value)
>>>x = x + 1 
>>>print x 
6

So before you can update a variable, you have to initialize it, usually with simple assignment but in our case we’ve used built-in Python function called raw_input that you’ve already met in our previous lessons.

After initialization of variable now we can update variable by adding 1 and this is called an increment, while subtracting by 1 is called decrement.