Unit 2 Python Programming Notes | AKTU Notes

Conditional Blocks

Conditional blocks are sections of code that run only when certain conditions are true. They help programs make decisions.

if statement

The if statement checks a condition and runs code only if that condition is True.

Example:

x = 10

if x > 5:

    print("x is greater than 5")

Explanation: This will print the message because x (10) is indeed greater than 5.

else statement

The else statement comes after if and runs when the if condition is False.

Example:

x = 3

if x > 5:

    print("x is greater than 5")

else:

    print("x is 5 or smaller")

Explanation: This will print "x is 5 or smaller" because 3 is not greater than 5.

elif statement (else if)

elif (short for "else if") checks another condition when the previous conditions were False.

Example:

x = 5

if x > 5:

    print("x is greater than 5")

elif x == 5:

    print("x is exactly 5")

else:

    print("x is smaller than 5")

Explanation: This will print "x is exactly 5" because the first condition is False but the second is True.

Important Notes

• - Conditions must end with a colon (:)
• - The code to run must be indented (usually 4 spaces)
• - You can have multiple elif statements
• else comes last and doesn't need a condition
• - Conditions can use comparison operators like ==, !=, <, >, <=, >=

Example

temperature = 85

if temperature > 100:

    print("Danger! Overheating!")

elif temperature > 80:

    print("Warning: High temperature")

elif temperature > 50:

    print("Normal operating range")

else:

    print("Warning: Low temperature")

This shows how conditional blocks can be used to monitor systems in engineering applications.

Simple For Loop

A for loop repeats code for each item in a sequence (like a list, string, or range).

Basic Syntax:

for item in sequence:

    # do something with item

For Loop with Range

range() creates a sequence of numbers for the loop to go through.

Examples:

# Loop from 0 to 4

for i in range(5):

    print(i)  # prints 0,1,2,3,4

# Loop from 2 to 6

for i in range(2, 7):

    print(i)  # prints 2,3,4,5,6

# Loop from 0 to 10 in steps of 2

for i in range(0, 11, 2):

    print(i)  # prints 0,2,4,6,8,10

For Loop with Strings

You can loop through each character in a string.

Example:

word = "engineer"

for letter in word:

    print(letter)

# prints e,n,g,i,n,e,e,r (each on new line)

For Loop with Lists

You can loop through each item in a list.

Example:

tools = ["hammer", "wrench", "screwdriver"]

for tool in tools:

    print(f"Use the {tool}")

# prints each tool name with "Use the" before it

For Loop with Dictionaries

Dictionaries need special methods to loop through keys, values, or both.

Examples:

car = {"brand": "Toyota", "model": "Corolla", "year": 2020}

# Loop through keys

for key in car.keys():

    print(key)  # prints brand, model, year

# Loop through values

for value in car.values():

    print(value)  # prints Toyota, Corolla, 2020

# Loop through both (items)

for key, value in car.items():

    print(f"{key}: {value}")

# prints brand: Toyota, model: Corolla, year: 2020

Important Notes

• - Always end the for statement with a colon (:)
• - The loop code must be indented
• - You can use break to stop the loop early
• - Use continue to skip to the next item
• - You can use else: after a for loop (runs if loop completes normally)

Example

# Calculate total resistance in parallel circuit

resistances = [10, 20, 30]  # in ohms

total = 0

for r in resistances:

    total += 1/r

equivalent_resistance = 1/total

print(f"Equivalent resistance: {equivalent_resistance:.2f} ohms")

This shows how for loops can be used in engineering calculations.

Python While Loops

1. What is a While Loop?

A while loop repeats a block of code as long as a condition is true. Unlike for loops that run for a set number of times, while loops run until the condition becomes false.

2. Basic Syntax

while condition:

    # code to execute

    # remember to update the condition

3. Simple Example

count = 0

while count < 5:

    print(f"Count is {count}")

    count += 1  # Important: Don't forget to update the counter!

Output: Prints "Count is 0" to "Count is 4"

4. Key Features

• - Condition Check: The loop checks the condition before each iteration
• - Infinite Loops: If the condition never becomes false, the loop runs forever
• - Control Statements: You can use break to exit or continue to skip to next iteration

5. Examples

a) Sensor Data Reading

temperature = 25

while temperature < 100:

    print(f"Current temperature: {temperature}°C")

    temperature += 15  # Simulating temperature rise

    if temperature > 80:

        print("Warning: Approaching critical temperature!")

print("System overheating! Shutting down...")

b) User Input Validation

while True:

    user_input = input("Enter engine RPM (800-6000): ")

    if user_input.isdigit() and 800 <= int(user_input) <= 6000:

        print("Valid RPM entered")

        break

    else:

        print("Invalid input! Try again.")

c) Convergence Calculation

tolerance = 0.0001

error = 1.0

x = 2.0  # Initial guess for square root of 4

while error > tolerance:

    new_x = 0.5 * (x + 4/x)  # Newton's method

    error = abs(new_x - x)

    x = new_x

    print(f"Current estimate: {x:.6f}, Error: {error:.6f}")

print(f"\nFinal square root approximation: {x:.6f}")

6. Common Mistakes

• - Forgetting to update the variable in the condition (causes infinite loop)
• - Using == instead of = when you mean to assign a value
• - Over-complicating conditions that could be simpler

7. While vs For Loops

While Loop	For Loop
Use when you don't know how many iterations are needed	Use when you know how many times to repeat
Runs until condition is false	Runs for each item in a sequence
Risk of infinite loops	No risk of infinite loops

8. Advanced Techniques

• - While-else: The else block executes when the condition becomes false
• - Nested while loops: While loops inside other while loops
• - Flag variables: Using boolean variables to control loop execution

Python Loop Manipulation: pass, continue, break, and else

Introduction to Loop Control Statements

These statements help you control the flow of loops in Python. They work with both for and while loops.

The pass Statement

This is a null operation - nothing happens when it executes.

When to use: When you need a statement for syntax purposes but don't want any action.

for i in range(5):

    if i == 3:

        pass  # Do nothing

    print(i)

# Output: 0 1 2 3 4

Engineering Example: Placeholder for future sensor reading implementation

while True:

    sensor_reading = get_sensor_data()

    if sensor_reading < 0:

        pass  # Will implement error handling later

    else:

        process_data(sensor_reading)

The continue Statement

Skips the rest of the current loop iteration and moves to the next one.

for i in range(1, 6):

    if i % 2 == 0:

        continue  # Skip even numbers

    print(f"Processing odd number: {i}")

# Output: Processing odd number: 1, 3, 5

Engineering Example: Skip invalid measurements

measurements = [12.5, -1, 15.2, 0, 18.7]

for m in measurements:

    if m <= 0:

        continue  # Skip invalid measurements

    analyze_measurement(m)

The break Statement

Exits the loop completely, skipping all remaining iterations.

for i in range(10):

    if i == 5:

        break  # Exit loop when i reaches 5

    print(i)

# Output: 0 1 2 3 4

Engineering Example: Emergency shutdown when critical threshold reached

while True:

    temperature = get_temperature()

    if temperature > 100:

        print("Critical temperature reached! Shutting down.")

        break

    process_temperature(temperature)

The else Clause in Loops

Executes only if the loop completes normally (not terminated by break).

for i in range(5):

    if i == 10:

        break

    print(i)

else:

    print("Loop completed normally")

# Output: 0 1 2 3 4

#         Loop completed normally

Engineering Example: Check if all tests passed

test_results = [True, True, True, True]

for result in test_results:

    if not result:

        print("Test failed! Stopping.")

        break

else:

    print("All tests passed successfully!")

Comparison Table

Statement	Effect	When to Use
pass	Does nothing	Placeholder for future code
continue	Skips current iteration	When you want to skip specific items
break	Exits the loop completely	When you need to stop processing
else	Runs after normal completion	For post-loop checks

Combined Example

# Process engineering data with all control statements

data = [2.5, 3.8, -1, 4.2, 0, 5.1, 6.7, 999]

for value in data:

    if value == 999:  # Sentinel value

        print("Termination signal received")

        break

    elif value <= 0:

        print(f"Invalid value {value} skipped")

        continue

    elif value > 5:

        pass  # Will handle high values later

    else:

        print(f"Processing normal value: {value}")

else:

    print("All data processed normally")

print("Data processing complete")

Programming Using Python Conditional and Loop Blocks

Introduction to Control Structures

Control structures help you control the flow of your program's execution. There are two main types:

• - Conditional blocks (if, elif, else) - for decision making
• - Loop blocks (for, while) - for repeating actions

Conditional Blocks

a) if statement

temperature = 85

if temperature > 100:

    print("System overheating!")

This checks if temperature exceeds 100 and prints a warning if true.

b) if-else statement

voltage = 220

if voltage >= 200 and voltage <= 240:

    print("Voltage within normal range")

else:

    print("Voltage out of range!")

This checks voltage and provides different outputs for normal and abnormal conditions.

c) if-elif-else ladder

rpm = 3500

if rpm > 5000:

    print("Danger! Critical speed")

elif rpm > 4000:

    print("Warning! High speed")

elif rpm > 3000:

    print("Approaching limit")

else:

    print("Normal operating range")

This checks multiple conditions in sequence.

Loop Blocks

a) for loop

# Calculate sum of resistances in a circuit

resistances = [10, 20, 30, 40]

total = 0

for r in resistances:

    total += r

print(f"Total resistance: {total} ohms")

b) while loop

# Countdown timer

time_left = 10

while time_left > 0:

    print(f"Countdown: {time_left}")

    time_left -= 1

print("Launch!")

Combining Conditionals and Loops

Example 1: Data Validation

measurements = [12.5, -1, 15.2, 0, 18.7]

valid_readings = 0

for m in measurements:

    if m <= 0:

        print(f"Invalid reading: {m}")

        continue

    valid_readings += 1

    print(f"Processing valid reading: {m}")

print(f"Total valid readings: {valid_readings}")

Example 2: Finding Prime Numbers

# Check if a number is prime

num = 17

is_prime = True

for i in range(2, num):

    if num % i == 0:

        is_prime = False

        break

if is_prime and num > 1:

    print(f"{num} is a prime number")

else:

    print(f"{num} is not a prime number")

Nested Control Structures

# Temperature monitoring system

temperatures = [85, 92, 78, 105, 88]

critical_count = 0

for temp in temperatures:

    if temp > 90:

        print(f"High temperature alert: {temp}°C")

        if temp > 100:

            critical_count += 1

            print("CRITICAL! Immediate action required")

    else:

        print(f"Normal temperature: {temp}°C")

print(f"Total critical alerts: {critical_count}")

Practical Engineering Applications

• - Sensor data processing: Filter valid/invalid readings
• - System monitoring: Check multiple parameters continuously
• - Simulations: Repeat calculations until convergence
• - Control systems: Implement decision logic for actuators
• - Data analysis: Process large datasets with conditional checks

Best Practices

• - Keep conditions simple and readable
• Avoid deeply nested structures (more than 3 levels)
• - Use meaningful variable names in conditions
• - Add comments for complex conditions
• - Test edge cases in your conditions
• - Ensure loops have clear termination conditions

Common Mistakes to Avoid

• - Forgetting colons (:) after conditions and loops
• - Missing indentation for blocks
• - Creating infinite loops (while True without break)
• - Using = (assignment) instead of == (comparison)
• - Not updating variables used in loop conditions