Python For Loops

Python For loop is used for sequential traversal i.e. it is used for iterating over an iterable like String, Tuple, List, Set or Dictionary.

In Python, there is no C style for loop, i.e., for (i=0; i<n; i++). There is “for” loop which is similar to each loop in other languages. Let us learn how to use for in loop for sequential traversals

Note: In Python, for loops only implements the collection-based iteration.

For Loops Syntax

for var in iterable:
    # statements

Flowchart of for loop

Here the iterable is a collection of objects like lists, tuples. The indented statements inside the for loops are executed once for each item in an iterable. The variable var takes the value of the next item of the iterable each time through the loop.

Examples of For Loops in Python

Example 1: Using For Loops in Python List

Python3

# Python program to illustrate
# Iterating over a list
l = ["geeks", "for", "geeks"]
for i in l:
    print(i)

Output:

Geeks
for
geeks

Example 2: Using For Loops in Python Dictionary

Python3

# Iterating over dictionary
print("Dictionary Iteration")
d = dict()
d['xyz'] = 123
d['abc'] = 345
for i in d:
    print("% s % d" % (i, d[i]))

Output:

Dictionary Iteration
xyz  123
abc  345

Example 3: Using For Loops in Python String

Python3

# Iterating over a String
print("String Iteration")
s = "Geeks"
for i in s:
    print(i)

Output:

String Iteration
G
e
e
k
s

Loop Control Statements

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed. Python supports the following control statements.

Continue Statement in Python

Python continue Statement returns the control to the beginning of the loop.

Example: Python for Loop with Continue Statement

Python3

# Prints all letters except 'e' and 's'
for letter in 'geeksforgeeks':
    if letter == 'e' or letter == 's':
        continue
    print('Current Letter :', letter)

Output:

Current Letter : g
Current Letter : k
Current Letter : f
Current Letter : o
Current Letter : r
Current Letter : g
Current Letter : k

Break Statement in Python

Python break statement brings control out of the loop.

Example: Python For Loop with Break Statement

Python3

for letter in 'geeksforgeeks':

    # break the loop as soon it sees 'e'
    # or 's'
    if letter == 'e' or letter == 's':
        break

print('Current Letter :', letter)

Output:

Current Letter : e

Pass Statement in Python

The pass statement to write empty loops. Pass is also used for empty control statements, functions, and classes.

Example: Python For Loop with Pass Statement

Python3

# An empty loop
for letter in 'geeksforgeeks':
    pass
print('Last Letter :', letter)

Output:

Last Letter : s 

range() function in Python

Python range() is a built-in function that is used when a user needs to perform an action a specific number of times. range() in Python(3.x) is just a renamed version of a function called xrange() in Python(2.x). 

The range() function is used to generate a sequence of numbers. Depending on how many arguments the user is passing to the function, user can decide where that series of numbers will begin and end as well as how big the difference will be between one number and the next.range() takes mainly three arguments. 

• start: integer starting from which the sequence of integers is to be returned
• stop: integer before which the sequence of integers is to be returned. 
  The range of integers end at stop – 1.
• step: integer value which determines the increment between each integer in the sequence 

Example: Python for loop with range function

Python3

# Python Program to
# show range() basics

# printing a number
for i in range(10):
    print(i, end=" ")

# performing sum of first 10 numbers
sum = 0
for i in range(1, 10):
    sum = sum + i
print("\nSum of first 10 numbers :", sum)

Output:

0 1 2 3 4 5 6 7 8 9 
Sum of first 10 numbers : 45

For loop in Python with else

In most programming languages (C/C++, Java, etc), the use of else statements has been restricted with the if conditional statements. But Python also allows us to use the else condition with for loops. 

Note: The else block just after for/while is executed only when the loop is NOT terminated by a break statement 

Python3

# Python program to demonstrate
# for-else loop

for i in range(1, 4):
    print(i)
else:  # Executed because no break in for
    print("No Break\n")

Output:

1
2
3
No Break

Note: For more information refer to our Python for loop with else tutorial.