Python For Loop

Before we start talking about Python for loop, let's briefly understand-What is for loop ?

The for loop in Python is used to iterate over sequences or iterable objects. This looping construct allows you to perform repetitive operations on a set of items.

The for and while loops are the two main looping constructs in Python that allow you to repeatedly repeat a block of code.

In this tutorial, we will go over the fundamentals of Python for loops. We'll also show you how to use the range type to generate a number sequence, as well as break and continue statements to change the flow of a loop. We will also address a few FAQs on Python for loop.

Python for Loop

The for loop in Python iterates over the items in a sequence and executes a block of statements repeatedly.

The Python for loop is written as follows:

for item in sequence:
  statements

The for statement begins with the for keyword, followed by a variable (item) to which each item of the sequence is assigned (loop control target), the in keyword, and finally the sequence. Each conditional statement is followed by a colon (:).

The statements block begins with an indentation and ends with the first line that is not indented. Most people prefer a 4-space or 2-space indentation. The official Python Code Style Guide recommends using 4-space per indentation level and avoiding mixing tabs and spaces for indentation.

Here is an example:

berries = ["Blueberry", "Raspberry", "Strawberry"]

for berry in berries:
  print(berry)

Output

Blueberry
Raspberry
Strawberry

It is possible to iterate over any sequence, such as a string, list, dictionary, or tuple.
We're iterating through the characters in the string 'linux' in the code below:

for x in 'linux':
  print(x)

Output

l
i
n
u
x

The variable is assigned to the key when looping through a dictionary:

berries = {'Blueberry': 100, 'Raspberry': 125, 'Strawberry': 150}

for key in berries:
  print(key)

Output

Blueberry
Raspberry
Strawberry

Use the key's index to access the dictionary's value:

berries = {'Blueberry': 100, 'Raspberry': 125, 'Strawberry': 150}

for key in berries:
  print(berries[key])

The values() method is another way to loop through the dictionary's values:

berries = {'Blueberry': 100, 'Raspberry': 125, 'Strawberry': 150}

for value in berries.values():
  print(value)

The output of both examples is the same:

Output

100
125
150

The range() Constructor

The Python range() constructor allows you to generate a sequence of integers by specifying the range's start and end points. In Python 2 and 3, range() behaves differently. Python 3 is used in this tutorial.

range() is commonly used in conjunction with the for loop to iterate over a sequence of numbers. This is the Python equivalent of a for loop in C.

When only one argument is provided, range returns a sequence of numbers, each one increasing by one from 0 to argument - 1:

for i in range(3):
  print(i)

Output

0
1
2

When given two arguments, range returns a sequence of numbers, each one incremented by one, beginning with the first argument and ending with the second argument - 1:

for i in range(3, 5):
  print(i)

Output

3
4

The third argument allows you to specify an increment:

for i in range(0, 16, 5):
  print(i)

Output

0
5
10
15

Nested for Loop

A nested loop is a loop inside another loop. They are frequently used to handle iterable objects that contain iterable elements:

for i in range(0, 6):
  for j in range(0, 6):
    print('%d + %d = %d' % (i, j, i+j))

Output

0 + 0 = 0
0 + 1 = 1
0 + 2 = 2
...
5 + 3 = 8
5 + 4 = 9
5 + 5 = 10

The break and continue Statements

The break and continue statements allow you to control how the for loop is executed.

break Statement

The break statement ends the current loop and transfers control to the statement that follows it. The break statement terminates the innermost loop when used within a nested loop.

In the following example, we use the if statement to end the loop execution when the current iterated item equals 'Raspberry':

for i in ["Blueberry", "Raspberry", "Strawberry"]:
  if i == "Raspberry":
    break
  print(i)

Output

Blueberry

continue Statement

The continue statement exits the current loop iteration and transfers programme control to the next loop iteration. Only the current iteration of the loop is skipped; the loop is not terminated.

We are iterating through a set of numbers in the following example. When the current iterated item equals '3,' the continue statement returns execution to the beginning of the loop and continues with the next iteration:

for i in range(1, 6):
  if i == 3:
    continue
  print(i)

Output

1
2
4
5

The else Clause

The for loop in Python can have an optional else clause.

When the loop completes normally, i.e. when all iterables are exhausted, the else clause is executed:

for i in ["Blueberry", "Raspberry", "Strawberry"]:
  print(i)
else:
  print('Loop completed.')

Output

Blueberry
Raspberry
Strawberry
Loop completed.

The else clause is not executed when the loop is terminated with a break or continue statement:

for i in ["Blueberry", "Raspberry", "Strawberry"]:
  if i == "Raspberry":
    break
  print(i)
else:
  print('Loop completed.')

Output

Blueberry

FAQs on Python For Loop

Conclusion

The Python for loop is used to execute a block of code for a set number of times.

If you have any queries, please leave a comment below and we’ll be happy to respond to them.