Intro to Python
Learn Python

Loops

This section covers:
for
loops
while
loops
Using
break
and
continue
Computers are often used to automate repetitive tasks. Python has two types of loops that can be used to execute instructions repeatedly: the
for
loop and the
while
loop.

The
for
loop

The
for
loop is useful for iterating over a sequence.

Here is a simple program that prints each number in a list and then prints “Done!”
my_favorite_numbers = [2, 8, 100, -23]
for
num
in
my_favorite_numbers:
print
(num)
print
('Done!')

You can also use
range
to iterate over a sequence of numbers. The following code will print the numbers 0 through 4.
for
i
in
range
(5):
print
(i)

Here is the basic structure of a
for
loop. Note the indentation used to indicate the instructions that should be repeated.
for
<variable>
in
<sequence>:
<body: code to be repeated for each element in the sequence>
<code to run after iterating through the sequence>
The body will be run once for each element in the sequence. In the body, you can refer to the current element using the name of the variable you provide between the
for
and the
in
.

The
while
loop

The
while
loop is used to repeatedly execute instructions as long as a boolean condition is met.

Here is a simple program that uses a
while
loop to count down from 5 and then prints “Blastoff!”
n =
5
while
n >
0
:
print
(n)
n = n -
1
print
(
'Blastoff!'
)

Here is the basic structure of a
while
loop. Note the indentation used to indicate the instructions that should be repeated.
while
<condition>:
<body: code to be repeated while condition is true>
<code to run when the condition is no longer true>

Using
break
and
continue

The
break
statement is used to exit early from a
for
or
while
loop.

Here is an example of a program that repeatedly takes the user’s input and prints it out until the user types “done”.
while
True
:
line = input('Type a word: ')
if
line == 'done':
break
print
(line)
print
(
'Done!'
)

The
continue
statement is used to skip the rest of the loop body and jump back to the
for
or
while
statement.

Here is an example of a program that prints all the cheeses except for "Parmesan”.
cheeses = ['Cheddar', 'Edam', 'Gouda']
for
cheese
in
cheeses:
if
cheese == 'Edam':
continue
print
(cheese)

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Status
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for
and
while
loops
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break
and
continue
statements
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