Control flow tools in Python allow you to manage the execution flow of your program. These tools include various statements and constructs that help in decision making, looping, and managing the flow of the program. In this section, we will cover the following control flow tools:

1. break Statement
2. continue Statement
3. pass Statement
4. else Clause in Loops
5. Nested Loops

The break statement is used to exit a loop prematurely. When the break statement is executed, the loop is terminated, and the control flow of the program moves to the statement immediately following the loop.

Explanation:

• The loop iterates from 0 to 9.
• When i equals 5, the break statement is executed, and the loop terminates.
• Output: 0 1 2 3 4

The continue statement is used to skip the current iteration of a loop and move to the next iteration. When the continue statement is executed, the remaining code inside the loop is skipped for the current iteration.

Explanation:

• The loop iterates from 0 to 9.
• When i is even, the continue statement is executed, and the loop skips to the next iteration.
• Output: 1 3 5 7 9

The pass statement is a null operation; it does nothing when executed. It is used as a placeholder for future code. When the pass statement is executed, nothing happens, but it can be useful in situations where a statement is syntactically required.

Explanation:

• The loop iterates from 0 to 4.
• When i equals 3, the pass statement is executed, and nothing happens.
• Output: 0 1 2 3 4

Python allows an else clause to be used with loops. The else clause is executed when the loop terminates normally (i.e., not by a break statement).

Explanation:

• The loop iterates from 0 to 4.
• After the loop completes, the else clause is executed.
• Output: 0 1 2 3 4 Loop completed without break

Explanation:

• The loop iterates from 0 to 4.
• When i equals 3, the break statement is executed, and the loop terminates.
• The else clause is not executed because the loop was terminated by a break statement.
• Output: 0 1 2

Nested loops are loops within loops. The inner loop is executed completely for each iteration of the outer loop.

Explanation:

• The outer loop iterates from 0 to 2.
• For each iteration of the outer loop, the inner loop iterates from 0 to 1.
• Output:

  i = 0, j = 0
  i = 0, j = 1
  i = 1, j = 0
  i = 1, j = 1
  i = 2, j = 0
  i = 2, j = 1
  

Write a program that finds the first number in a list that is divisible by 7 and prints it. Use the break statement to exit the loop once the number is found.

Solution:

Write a program that prints all the numbers from 1 to 10, except those that are divisible by 3. Use the continue statement to skip the numbers divisible by 3.

Solution:

Write a program that checks if a list of numbers contains any negative numbers. If a negative number is found, print "Negative number found" and exit the loop. If no negative numbers are found, print "All numbers are positive".

Solution:

In this section, we covered essential control flow tools in Python, including break, continue, and pass statements, the else clause in loops, and nested loops. These tools are crucial for managing the flow of your program and making it more efficient and readable. Practice using these tools in different scenarios to become more comfortable with them. In the next section, we will delve into list comprehensions, a powerful feature for creating and manipulating lists in Python.