iteration updating variables common pattern in assignment statements is an assignment statement that updates variablewhere the new value of the variable depends on the old this means "get the current value of xadd and then update with the new value if you try to update variable that doesn' existyou get an errorbecause python evaluates the right side before it assigns value to xx nameerrorname 'xis not defined before you can update variableyou have to initialize itusually with simple assignmentx updating variable by adding is called an incrementsubtracting is called decrement the while statement computers are often used to automate repetitive tasks repeating identical or similar tasks without making errors is something that computers do well and people do poorly because iteration is so commonpython provides several language features to make it easier one form of iteration in python is the while statement here is simple program that counts down from five and then says "blastoff!