Control Statements in Python

Last Updated: 6th October, 2024

Control statements direct the flow of a Python program's execution. They introduce logic, decision-making, and looping. Key control statements in Python include if/else, for/while, break/continue, and pass. Let's get into our lesson to understand these concepts clearly.

What are Control Statements in Python?

Flow control in Python is the process of controlling and directing the progression of program execution by utilizing conditional statements , iterative loops 🔁, and reusable functions 🔄. It helps govern a program's logic and coherence, permitting code to execute only when certain predefined conditions have been satisfied. In particular, flow control allows a program to make decisions :thinking: and perform repetitive tasks 🔁.

Conditional statements like if-else tests enable a program to evaluate expressions and execute code only if certain conditions are true or false. Loops like for and while loops  enable a program to reiterate through a block of code multiple times. Functions 🔄 allow a program to encapsulate and call a code block from multiple locations.

Together, conditional statements , loops , and functions  provide the mechanism to control the flow of a program and craft complex logic in a readable and maintainable fashion. Flow control is a foundational concept in programming that allows one to craft programs that can make judgments , perform recurring actions , and execute in a nonlinear manner. For these reasons, flow control is essential for creating Python programs that are versatile, capable, and resilient.

Let’s look at the control statements in python with examples for understanding:

Reservation Checking in Restaurant

• A restaurant manager checks if a customer has a reservation. If the customer has a reservation, they are shown to their table.
• 🧐 ❓ If not, the restaurant checks if there are any available tables.
• 🪑 ✅ If there are available tables, the customer is seated.
• ⛔ ❌ If not, the customer is told that the restaurant is fully booked and cannot accommodate them.

Let's visualize this example first, then talk about it using Python code.

Importance of Control Statements in Python

We require flow control to customize his program's flow and make it operate precisely how he wants it to. Moreover, he makes use of this in daily life. For instance, he determines if he can safely cross a road before we do so.🚦If not, we wait until the situation is safe before moving further. Just deciding which sentence should run before or after another, how the code should behave in specific circumstances, etc., is all he is doing. With Python, we have elegant, clear techniques to create flow control. 💻 Let's talk about them.

Types of Control Statements in Python

In Python, loops and conditional statements control code execution on a specific condition. There are two types of control statements in python, as discussed below:

Conditional Control Statements in Python

"Conditional" refers to something dependent on a specific condition or circumstance. In programming, a conditional statement executes different codes based on whether a particular condition is true or false. 💡Three conditional statements will help him. Let's help him understand each one with an example.

if condition

The if statement checks whether a given condition is true. If it evaluates to True, the associated code block is executed. It introduces decision-making in the flow of a program, allowing conditional execution of code.

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This code is an example of an if statement. It checks if the value stored in the variable "age" is greater than or equal to 18. If the statement is true, the code will print, "You are eligible to vote.”

if else condition

The if-else statement extends the basic if by providing an alternative code block when the condition is false. This ensures that one of two possible actions is always executed depending on the condition’s result.

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In this example, x is set to 5, using an if-else condition to test whether x is greater than 10. If x is greater than 10, it will print "x is greater than 10"; otherwise, it will print "x is not greater than 10".

if elif else condition

The if-elif-else structure allows checking multiple conditions sequentially. It evaluates conditions one by one; once a condition is true, its corresponding block is executed, and the remaining conditions are ignored. The else block runs only if none of the conditions are true.

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In this example, x is set to 5, and an if-else condition is used to test whether x is greater than 10. If x is greater than 10, it will print "x is greater than 10", else it will try if x is greater than 20; if x is greater than 20, it will print "x is greater than 20", otherwise it will print "x is not greater than 10 and 20".

Loop Control Statements in Python

Loop control statements in python are control structures in programming that allow a piece of code to be executed repeatedly, either a specific number of times or until a particular condition is met ⏰.

For Loop

The for loop is used to iterate over a sequence (such as a list, tuple, or string) or a range of numbers. It repeats a block of code for each element in the sequence, making it ideal for iterating through known ranges or collections.

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This program uses a for loop to iterate through numbers from 0 to 10. For each iteration, the value of i is printed. The for loop will continue until it reaches 11, which is not included in the range.

While Loop

The while loop continues to execute a block of code as long as a specified condition remains true. It is useful when the number of iterations is not predetermined, and the loop should keep running until the condition changes.

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This program prints the numbers from 1 to 10 using a while loop. The loop starts at 1 and continues until it reaches 10. The loop terminates when the value of num is greater than 10.

Advanced Control Statements in Python

Break Statement: The break statement is used to exit a loop prematurely when a specific condition is met. This helps avoid unnecessary iterations.

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This will print numbers from 0 to 4 and exit the loop when i equals 5.

Continue Statement: The continue statement skips the current iteration and moves on to the next iteration of the loop.

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This will print 0, 1, 2, 4, skipping 3.

Pass Statement: The pass statement is a placeholder that does nothing. It's useful when a statement is syntactically required but you don't want to execute any code at that point.

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Else with Loops: Python supports the else clause in loops. The else block is executed when the loop completes normally (without encountering break).

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Nested Loops: Loops can be nested inside other loops, which is useful for working with multidimensional data structures like matrices.

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This prints all combinations of i and j.

Exception Handling Control Statements in Python

Python offers control over unexpected errors through try, except, and finally blocks. This ensures that your program continues to run smoothly even when something goes wrong.

Try-Except Block: It is used to catch exceptions and execute alternative code when an error occurs.

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This handles the case where the user inputs zero or an invalid number.

Finally Block: The finally block is always executed, regardless of whether an exception occurred or not. It's often used to clean up resources.

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💡 Did You know?

In Python, you can check multiple conditions simultaneously using multiple comparisons. This is different from other programming languages, where you cannot randomly chain comparison operators and instead follow a particular order of operators.

Conclusion

This lesson provides an overview of control statements in Python, including their importance and types. Python control statements allow for logic, decision-making, and looping in a program. Conditional statements like if/else and loops like for/while are discussed, along with their syntax and examples 

Key Takeaways

1. If a specified condition evaluates True, the if statement allows you to execute a code block. You can use if statements to execute code only when certain conditions are met. :woman_tipping_hand:
2. The for statement allows you to iterate over a sequence, like a list or string, and execute a block of code once for each element in the sequence; for statements are helpful when you want to repeat an action a specific number of times. 🔁
3. The while statement allows you to execute a code block repeatedly as long as a specified condition remains True. While statements will continue looping as long as the condition evaluates to True, you need to ensure there is a way for the condition to become False to prevent an infinite loop eventually. 🔂
4. To properly execute, all control statements in Python must be indented at the same level. The indentation level determines which statements are part of the control statement block. 📏
5. In addition to the three main control statements, Python supports break and continue statements. The break statement exits a for or while loop immediately. The continue statement skips the rest of the current iteration of the loop and jumps back to the top of the loop. ⛔
6. Control statements are a fundamental part of any Python program and allow you to control the flow and logic of your code. Using the appropriate python control statements, you can create complex and robust programs in Python. 🚀

Quiz

1. What is the purpose of the 'if' statement?
   1. Execute code if a condition is true 
   2. Execute code if a condition is false 
   3. Execute code no matter what 
   4. Execute code multiple times

Answer: A) Execute code if a condition is true

2. How do you use if statements in Python?
   1. if condition: 
   2. if: condition  
   3. if (condition): 
   4. Both A and C

Answer: D) Both A and C

3. What is an else statement used for?
   1. Execute code if a condition is true 
   2. Execute code if a condition is false 
   3. Execute code no matter what 
   4. Execute code multiple time

Answer: B) Execute code if a condition is false