Nested Loops and Loop Control

In the previous section, we learned about control structures and loops in Python. We explored conditional statements and different types of loops such as for and while loops. Now, let’s dive deeper into the concept of nested loops and how we can control them.

Nested Loops

A nested loop is a loop inside another loop. Just like nesting dolls, where one doll is enclosed inside another, nested loops function similarly. With each iteration of the outer loop, the nested loop completes its entire cycle.

Let’s take a look at an example to clarify the concept of nested loops:

“`python for x in range(1, 6): for y in range(1, 4): print(x, y) “`

In this code snippet, we have an outer loop that iterates from 1 to 5, and an inner loop that iterates from 1 to 3. The print statement within the inner loop will output the values of both x and y for each combination.

The output of the above code will be:

1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3
4 1
4 2
4 3
5 1
5 2
5 3

Notice how the inner loop completes its cycle for each iteration of the outer loop. Nested loops are useful when we need to perform operations on multiple dimensions or iterate through a multidimensional data structure like a matrix or a two-dimensional list.

Loop Control Statements

In addition to the basic loop constructs, Python provides several loop control statements that help in modifying the behavior of loops. These statements include break, continue, and pass.

The break statement is used to exit the loop prematurely. When encountered inside a loop, it terminates the loop execution and transfers the control to the statement immediately following the loop. Let’s see it in action:

“`python for num in range(1, 6): if num == 3: break print(num) “`

The output of the above code will be:

1
2

The loop terminates when the break statement is encountered, thus skipping the iteration where the value of num is 3.

The continue statement is used to skip the rest of the code block inside the loop for the current iteration and proceed to the next iteration. The control jumps back to the loop header and the next iteration begins. Let’s take a look at an example:

“`python for num in range(1, 6): if num == 3: continue print(num) “`

The output of the above code will be:

1
2
4
5

In this example, the continue statement skips the print statement for the iteration where the value of num is 3, and the control moves to the next iteration.

The pass statement is used as a placeholder when no action is required inside a loop. It acts as a null operation, meaning it does nothing. It is often used to prevent syntax errors when a code block is required but no action is needed. Here’s an example:

“`python for num in range(1, 6): if num % 2 == 0: pass else: print(num) “`

The output of the above code will be:

1
3
5

In this example, the pass statement doesn’t affect the flow of the loop. It simply allows the code to continue executing without any interruption.

Understanding and utilizing nested loops effectively along with loop control statements can greatly enhance your ability to handle complex problems and manipulate data structures in Python.

Congratulations! You’ve now learned about nested loops and loop control in Python. Take some time to practice these concepts and explore more complex examples to solidify your understanding. In the next section, we will cover another important topic, functions in Python.