For Loops

When we have a list of things to loop through, we can construct a definite loop using for statement. We call the while statement an indefinite loop because it simply loops until some condition becomes False whereas the for loop is looping through a known set of items so it runs through as many iterations as there are items in the set.

The syntax of a for loop is similar to the while loop in that there is a for statement and a loop body:

movies =['Terminator 1','Terminator 2', 'Terminator 3' ]
for movie in movies:
    print 'I watched:', movie
print 'Done!'

In Python the variable movies is a list of three strings and the for loop goes through the list and executes the body once for each of the three strings in the list resulting in this output:

I watched: Terminator 1
I watched: Terminator 2
I watched: Terminator 3
Done!

Translating for loop to English: Run the statements in the body of the for loop once for each movie in the set named movies

Looking at the for loop, for and in are reserved Python keywords, and movie and movies are variables.

for movie in movies:
 Print ‘I watched:’ , movie 

Movie is the iteration variable for the for loop. The variable movie changes for each iteration of the loop and controls when the for loop completes. The iteration variable steps successively through the three strings stored in movies variable.