Oct. 08, 2012

How to use Loops in Python

To keep a computer doing useful work we need repetition, looping back over the same block of code again and again. This post will describe the different kinds of loops in Python.

For Loop

The for loop that is used to iterate over elements of a sequence, it is often 
used when you have a piece of code which you want to repeat "n" number of time. 

It works like this: " for all elements in a list, do this "

Let's say that you have a list
computer_brands = ["Apple", "Asus", "Dell", "Samsung"]
for brands in computer_brands:
    print brands
That reads, for every element that we assign the variable brands, 
in the list computer_brands, print out the variable brands
numbers = [1,10,20,30,40,50]
sum = 0
for number in numbers:
    sum = sum + numbers
print sum
for i in range(1,10):
    print i


To break out from a loop, you can use the keyword "break". 
for i in range(1,10):
    if i == 3:
    print i


The continue statement is used to tell Python to skip the rest of the statements 
in the current loop block and to continue to the next iteration of the loop.
for i in range(1,10):
    if i == 3:
    print i

While Loop

The while loop tells the computer to do something as long as the condition is met
it's construct consists of a block of code and a condition. 

It works like this: " while this is true, do this "
computer_brands = ["Apple", "Asus", "Dell", "Samsung"]
i = 0
while i < len(computer_brands):
    print computer_brands(i)
    i = i + 1

That reads, as long as the value of the variable i is less than the length of the 
list (computer_brands), print out the variable name.
while True:
    answer = raw_input("Start typing...")
    if answer == "quit":
    print "Your answer was", answer

Let's show another example.

Here we set the variable counter to 0. 

For every time the while loop runs, the value of the counter is increased by 2. 

The while loop will run as long as the variable counter is less or equal with 100.
counter = 0
while counter <= 100:
    print counter
    counter + 2

Nested Loops

In some script you may want to use nested loops. 

A nested loop is a loop inside a loop. 
for x in range(1, 11):
    for y in range(1, 11):
        print '%d * %d = %d' % (x, y, x*y)

Recommended Python Training – DataCamp

For Python training, our top recommendation is DataCamp.

Datacamp provides online interactive courses that combine interactive coding challenges with videos from top instructors in the field.

Datacamp has beginner to advanced Python training that programmers of all levels benefit from.


Read more about:
Disclosure of Material Connection: Some of the links in the post above are “affiliate links.” This means if you click on the link and purchase the item, I will receive an affiliate commission. Regardless, PythonForBeginners.com only recommend products or services that we try personally and believe will add value to our readers.