Python For Loops

 

Python For Loops

A for loop is used for iterating over a sequence (that is either a list or a string).

With the for loop we can execute a set of statements, once for each item in a list or a string. 

Example:

fruits = ["apple", "banana", "cherry"]

for x in fruits:

  print(x)

OUTPUT:

apple

banana

cherry

Looping Through a String

Even strings are iterable objects, they contain a sequence of characters:

Example:

for x in "banana":
  print(x)

Output:

b

a

n

a

n

a

The range() Function

To loop through a set of code a specified number of times, we can use the range() function,

The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.

Example

for x in range(6):
  print(x)

OUTPUT:

0

1

2

3

4

5

Note:  range(6) is not the values of 0 to 6, but the values 0 to 5.

The range() function defaults to 0 as a starting value, however it is possible to specify the starting value by adding a parameter: range(2, 6), which means values from 2 to 6 (but not including 6):

Example

for x in range(2, 6):
  print(x)

OUTPUT: 

2

3

4

5

The range() function defaults to increment the sequence by 1, however it is possible to specify the increment value by adding a third parameter: range(2, 30, 3):

Example

#print the times table of 2.

for x in range(2, 21, 2):

  print(x)

Output:

2

4

6

8

10

12

14

16

18

20

Else in For Loop

The else keyword in a for loop specifies a block of code to be executed when the loop is finished:

Example

for x in range(6):
  print(x)
else:
  print("Finally finished!")

Output:

0

1

2

3

4

5

Finally finished!

Nested Loops

A nested loop is a loop inside a loop.

The "inner loop" will be executed one time for each iteration of the "outer loop":

Example:

#Print each adjective for every fruit:

adj = ["red", "big", "tasty"]

fruits = ["apple", "banana", "cherry"]

for x in adj:

  for y in fruits:

    print(x, y)

Output:

red apple
red banana
red cherry
big apple
big banana
big cherry
tasty apple
tasty banana
tasty cherry