Python For Loops

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

For Loops in Python

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. 

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

For Loops Syntax

for var in iterable:
    # statements

Flowchart of for loop

For Loop flowchart

Here the iterable is a collection of objects like lists, and 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 Python For Loop

Python For Loop with List

This code uses a for loop to iterate over a list of strings, printing each item in the list on a new line. The loop assigns each item to the variable I and continues until all items in the list have been processed.

Python3

# Python program to illustrate
# Iterating over a list
l = ["geeks", "for", "geeks"]

for i in l:
    print(i)

Output :

geeks
for
geeks

Python For Loop in Python Dictionary

This code uses a for loop to iterate over a dictionary and print each key-value pair on a new line. The loop assigns each key to the variable i and uses string formatting to print the key and its corresponding value.

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

Python For Loop in Python String

This code uses a for loop to iterate over a string and print each character on a new line. The loop assigns each character to the variable i and continues until all characters in the string have been processed.

Python3

# Iterating over a String
print("String Iteration")

s = "Geeks"
for i in s:
    print(i)

Output:

String Iteration
G
e
e
k
s

Python For Loop with a step size

This code uses a for loop in conjunction with the range() function to generate a sequence of numbers starting from 0, up to (but not including) 10, and with a step size of 2. For each number in the sequence, the loop prints its value using the print() function. The output will show the numbers 0, 2, 4, 6, and 8.

Python3

for i in range(0, 10, 2):
    print(i)

Output :

0
2
4
6
8

Python For Loop inside a For Loop

This code uses nested for loops to iterate over two ranges of numbers (1 to 3 inclusive) and prints the value of i and j for each combination of the two loops. The inner loop is executed for each value of i in the outer loop. The output of this code will print the numbers from 1 to 3 three times, as each value of i is combined with each value of j.

Python3

for i in range(1, 4):
    for j in range(1, 4):
        print(i, j)

Output :

1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3 

Python For Loop with Zip()

This code uses the zip() function to iterate over two lists (fruits and colors) in parallel. The for loop assigns the corresponding elements of both lists to the variables fruit and color in each iteration. Inside the loop, the print() function is used to display the message “is” between the fruit and color values. The output will display each fruit from the list of fruits along with its corresponding color from the colours list.

Python3

fruits = ["apple", "banana", "cherry"]
colors = ["red", "yellow", "green"]
for fruit, color in zip(fruits, colors):
    print(fruit, "is", color)

Output :

apple is red
banana is yellow
cherry is green

Python For Loop with Tuple

This code iterates over a tuple of tuples using a for loop with tuple unpacking. In each iteration, the values from the inner tuple are assigned to variables a and b, respectively, and then printed to the console using the print() function. The output will show each pair of values from the inner tuples.

Python3

t = ((1, 2), (3, 4), (5, 6))
for a, b in t:
    print(a, b)

Output :

1 2
3 4
5 6

Loop Control Statements

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

Python for Loop with Continue Statement

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

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

Python For Loop with Break Statement

Python break statement brings control out of the loop.

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

Python For Loop with Pass Statement

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

Python3

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

Output:

Last Letter : s 

Python for loop with range function

The Python range() function is used to generate a sequence of numbers. Depending on how many arguments the user is passing to the function, the 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 ends at a stop – 1.
• step: integer value which determines the increment between each integer in the sequence.

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

Else With For loop in Python

Python also allows us to use the else condition for loops. 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

Certainly! If you’re interested in learning more about Python For Loop with Else in Python, you might find the following article on GeeksforGeeks helpful: Python for loop with else tutorial. Check it out if you’d like to learn more!