Python for Statements (With Examples)

In Python, the for statement is a powerful and versatile construct used for iterating over sequences, collections, or any iterable object. It allows you to perform a specific set of actions for each item in the iterable, making it a fundamental tool for handling repetitive tasks efficiently. This tutorial will guide you through the various aspects of the for statement in Python, along with illustrative examples to help you grasp its usage effectively.

Table of Contents

1. Introduction to the for Statement
2. Basic Syntax of the for Statement
3. Iterating Through Lists
4. Iterating Through Strings
5. Iterating Through Dictionaries
6. Nested for Loops
7. The range() Function and Numeric Iteration
8. Using the enumerate() Function
9. List Comprehensions with for Statements
10. Exiting Loops Prematurely with break
11. Skipping Iterations with continue
12. Practical Examples
    • Example 1: Calculating the Sum of Numbers
    • Example 2: Finding the Longest Word in a List of Strings
13. Conclusion

1. Introduction to the for Statement

The for statement is one of the core control structures in Python that facilitates iterative processes. It allows you to iterate over a sequence of items, performing a set of actions for each item in the sequence. This sequence can be a list, tuple, string, dictionary, or any other iterable object.

2. Basic Syntax of the for Statement

The basic syntax of the for statement is as follows:

for item in iterable:
    # Code to execute for each item
    # ...

• item: This is a variable that takes the value of each item in the iterable during each iteration.
• iterable: This is the collection of items over which the loop iterates.

3. Iterating Through Lists

One of the most common use cases for the for statement is iterating through a list. Let’s see an example:

fruits = ['apple', 'banana', 'cherry', 'date']

for fruit in fruits:
    print(f"I like {fruit}s")

Output:

I like apples
I like bananas
I like cherries
I like dates

4. Iterating Through Strings

Strings are iterable in Python, which means you can use a for statement to iterate through each character in a string:

message = "Hello, Python!"

for char in message:
    print(char)

Output:

H
e
l
l
o
,

P
y
t
o
n
!

5. Iterating Through Dictionaries

When iterating through dictionaries, the for statement by default iterates through the keys. However, you can access both keys and values using the items() method:

student_grades = {'Alice': 85, 'Bob': 92, 'Charlie': 78}

for student in student_grades:
    print(f"{student} scored {student_grades[student]}")

# Using items() to iterate through keys and values
for student, grade in student_grades.items():
    print(f"{student} scored {grade}")

Output:

Alice scored 85
Bob scored 92
Charlie scored 78

Alice scored 85
Bob scored 92
Charlie scored 78

6. Nested for Loops

You can nest one or more for loops within another for loop to create more complex iterations. This is useful for iterating through multidimensional data structures like matrices or nested lists:

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

for row in matrix:
    for num in row:
        print(num, end=' ')
    print()  # Move to the next line after each row

Output:

1 2 3
4 5 6
7 8 9

7. The range() Function and Numeric Iteration

The range() function generates a sequence of numbers that can be used in for loops. It can take one, two, or three arguments: range(stop), range(start, stop), or range(start, stop, step).

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

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

Output:

0
1
2
3
4

2
4
6
8

8. Using the enumerate() Function

The enumerate() function pairs each item in an iterable with its index. This is useful when you need both the index and the item during iteration:

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

for index, fruit in enumerate(fruits):
    print(f"At index {index}: {fruit}")

Output:

At index 0: apple
At index 1: banana
At index 2: cherry

9. List Comprehensions with for Statements

List comprehensions provide a concise way to create lists using for statements. They allow you to generate new lists by applying an expression to each item in an existing iterable:

numbers = [1, 2, 3, 4, 5]
squared = [num ** 2 for num in numbers]
print(squared)  # Output: [1, 4, 9, 16, 25]

10. Exiting Loops Prematurely with break

The break statement is used to exit a loop prematurely based on a certain condition. It’s often used to terminate a loop when a specific value or condition is reached:

numbers = [10, 20, 30, 40, 50]

for num in numbers:
    if num > 30:
        break
    print(num)

Output:

10
20
30

11. Skipping Iterations with continue

The continue statement is used to skip the rest of the current iteration and proceed to the next one. It’s often used to exclude certain values from being processed within a loop:

numbers = [1, 2, 3, 4, 5]

for num in numbers:
    if num % 2 == 0:
        continue
    print(num)

Output:

1
3
5

12. Practical Examples

Example 1: Calculating the Sum of Numbers

Let’s say you want to calculate the sum of numbers from 1 to 10 using a for loop:

total = 0

for num in range(1, 11):
    total += num

print("Sum:", total)

Output:

Sum: 55

Example 2: Finding the Longest Word in a List of Strings

You have a list of

words and you want to find the longest word:

words = ['apple', 'banana', 'cherry', 'date']

longest_word = ''

for word in words:
    if len(word) > len(longest_word):
        longest_word = word

print("Longest word:", longest_word)

Output:

Longest word: banana

13. Conclusion

In this tutorial, we explored the power and versatility of the for statement in Python. We learned how to iterate through various types of iterables, work with nested loops, use the range() function for numeric iteration, employ the enumerate() function, and apply list comprehensions. Additionally, we saw how to control the flow of loops using the break and continue statements. Armed with this knowledge, you can now confidently use the for statement to efficiently handle repetitive tasks in your Python programs. Happy coding!