Control Flow Loops

While Loop

A while loop will repeat a block of statements while a condition is true. This code will print out the contents of the items in the list. This code uses a function called len , which is a built-in function that returns the length of a list or string.

listOfFruit = ['Apples', 'Oranges', 'Bananas']
x = 0
while x < len(listOfFruit):
print listOfFruit[x]
x = x + 1

For Loop

Python's for loop may be a bit different than what you're used to if you've programmed any C. The for loop is specialized to iterate over the elements of any sequence, like a list. So, we could re-write the example above using a for loop eliminating the counter x:

listOfFruit = ['Apples', 'Oranges', 'Bananas']
for item in listOfFruit:
print item

Much more graceful! You'll often see the for loop used instead of the while loop, even when you simply want to iterate a given number of times. To do this with the for loop, you can use the built-in function range. The range function returns a variable-size list of integers starting at zero. Calling range(4) will return the list [0, 1, 2, 3]. So, to have a for loop repeat 4 times, you simply can do:

for x in range(4):
print "this will print 4 times"

Break and Continue In Loops

You can stop a loop from repeating in its tracks by using the break statement. This code will print out " Loop " exactly two times, and then print " Finished ".

for x in range(10):
if x >= 2:
break
print "Loop"
print "Finished"

You can use the continue statement to make a loop stop executing its current iteration and skip to the next one. The following code will print out the numbers 0-9, skipping 4

for x in range(10):
if x == 4:
continue
print x

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