For Loop

What Will You Learn
This section teaches you how to use for loops in Python to iterate over sequences like lists, strings, ranges, and dictionaries. You'll understand loop structure, the role of the range() function, and how to use break, continue, and else within loops. These fundamentals are essential for repetitive tasks and data processing.

The for loop is one of the most essential tools for any programmer working with Python. It allows you to repeat a block of code a specific number of times or iterate over items in a sequence like a list, tuple, or string. Without loops, repetitive tasks would have to be written manually, making code inefficient and harder to maintain.

In this section, you'll learn exactly how for loops work, when to use them, and what makes them powerful and readable in Python. We'll cover basic syntax, practical variations, and common patterns. Whether you're iterating over numbers, indexes, or multiple sequences at once, mastering for loops is a must for writing clean and logical Python code.

What Is a For Loop in Python?

A for loop in Python is used to iterate over a sequence of values. It goes through each item, one at a time, and runs a block of code for each iteration. Unlike in many other programming languages, Python’s for loop doesn’t require manually initializing counters or managing the loop’s end condition — it works directly with iterables.

The loop uses the in keyword to iterate over a list, string, tuple, dictionary, or any iterable object. It’s clean, easy to read, and eliminates the need for traditional counting loops in most scenarios. Python also offers built-in functions like range() and enumerate() that enhance the power and flexibility of for loops. From traversing lists to parallel iteration, Python handles it efficiently.

Here are some common ways to use for loops in Python:

• Inline for loop (Python list comprehension). A concise way to generate lists using for.

squares = [x * x for x in range(5)]

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• For loop with index. Iterate using a range to access index and values.

    for i in range(len(items)):
        print(i, items[i])

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• Enumerate for loop. Use enumerate() to get index and value directly.

    for index, value in enumerate(items):
        print(index, value)

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• Backwards for loop. Iterate in reverse using reversed() or range().

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

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• Parallel for loop. Use zip() to iterate over two lists simultaneously.

    for name, score in zip(names, scores):
        print(f"{name}: {score}")

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How to Do a For Loop in Python?

To perform a for loop in Python, you use the for keyword followed by a variable name, the in keyword, and the iterable you want to loop through. The indented block of code below the loop runs once for each item in the sequence. Python automatically handles iteration and updates the loop variable with each new value. This makes the for loop ideal for working with lists, strings, dictionaries, ranges, and other iterable objects. The loop ends when the iterable is exhausted — you don't need to manually increment counters or check stop conditions. This approach leads to clean, readable code that is easy to write and understand. You can also use helper functions like range() or enumerate() to enhance the loop’s behavior.

How to Write a For Loop in Python?

Writing a for loop in Python is simple and consistent. You start with the for keyword, followed by a loop variable that represents the current item in the iteration. Then use the in keyword followed by the iterable (such as a list or range). A colon : marks the start of the loop block, and the indented code below runs for each element. The loop variable updates automatically on each pass. Here's an example:

    for fruit in ["apple", "banana", "cherry"]:
        print(fruit)

This loop prints each fruit in the list. The loop variable fruit takes on the value of each item in the list, one at a time.

You can also use the range() function to create a sequence of numbers. For example, range(5) generates numbers from 0 to 4. This is useful for iterating a specific number of times:

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

This loop prints numbers 0 to 4. The loop variable i takes on each value in the range, allowing you to perform actions based on the current index.

How to End a For Loop in Python?

A for loop in Python automatically ends when the iterable is fully consumed — no explicit condition or exit command is needed. However, if you want to stop the loop early, you can use the break statement. This is useful when a certain condition is met and there's no need to continue iterating. Another approach is using return if the loop is inside a function and you want to exit completely. You can also use a pass statement as a placeholder inside a loop if no action is required. Here's an example using break:

    for num in range(10):
        if num == 5:
            break
        print(num)

This loop stops when num reaches 5, printing only 0 to 4.

Common Mistakes Made by Beginners

1. Forgetting the colon at the end of the for line

Beginners often forget the colon : at the end of the for loop declaration, which leads to a SyntaxError.

Incorrect:

    for i in range(5)
        print(i)

Fix: Always add a colon.

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

2. Not using indentation

In Python, indentation defines code blocks. If you forget to indent the loop body, Python throws an IndentationError.

Incorrect:

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

Fix: Indent the body by 4 spaces or 1 tab.

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

3. Modifying the loop variable inside the loop

Changing the loop variable manually inside the loop may cause logical errors and confusion.

Problem:

    for i in range(5):
        i += 1
        print(i)

Fix: Let Python handle iteration. Use other variables if needed.

4. Using range() on a non-integer

Beginners mistakenly try to use range() with non-integer values, like floats or strings, which raises a TypeError.

Incorrect:

    for i in range(0, 5.5):
        print(i)

Fix: Ensure all arguments to range() are integers.

    for i in range(6):
        print(i)

5. Using break without a condition

Calling break with no conditional check ends the loop immediately, which may not be intended.

Problem:

    for i in range(10):
        print(i)
        break

Fix: Use break only inside a meaningful if condition.

6. Looping over an empty list or wrong iterable

Trying to iterate over None or an empty list won’t raise an error, but nothing will execute.

Problem:

    data = None
        for item in data:
        print(item)

Fix: Check that the iterable is not None or empty before the loop:

    if data:
        for item in data:
            print(item)

FAQ – For Loop in Python

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

    # For loop
    for i in range(5):
        print(i)

    # While loop
    i = 0
    while i < 5:
        print(i)
        i += 1

    for i in range(5):
        if i == 2:
            continue
        print(i)

    for item in reversed(my_list):
        print(item)

    for i in range(len(my_list)-1, -1, -1):
        print(my_list[i])

    data = {'a': 1, 'b': 2}
    for key in data:
        print(key)

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

    for key, value in data.items():
        print(key, value)

    for num in range(10):
        if num % 2 == 0:
            print(f"{num} is even")