06 🔄 Control Flow

Control flow determines the execution order of statements in a Python program. It includes conditional statements, loops, and exception handling, allowing programs to make decisions and repeat actions efficiently.

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🔹 4.1 Conditional Statements (if, elif, else)

Conditional statements allow Python to execute different blocks of code based on conditions.

✅ Basic if-else Statement

x = 10

if x > 0:
    print("Positive number")
elif x < 0:
    print("Negative number")
else:
    print("Zero")

Output: Positive number

🔹 Nested if Statements

age = 20

if age > 18:
    if age >= 21:
        print("Eligible for full privileges")
    else:
        print("Limited privileges")
else:
    print("Not eligible")

✅ Use Case: Decision trees in ML models, data validation, user authentication.

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🔹 4.2 Looping in Python

Loops allow repeating actions based on conditions.

🔹 for Loop (Iterating over Sequences)

numbers = [1, 2, 3, 4, 5]

for num in numbers:
    print(num)

Output:

1
2
3
4
5

✅ Use Case: Iterating over lists, tuples, dictionaries, and strings in data processing, ML datasets.

🔹 for Loop with range()

for i in range(1, 6):
    print(i)

Output:

1
2
3
4
5

✅ Use Case: Creating training epochs in machine learning models.

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🔹 while Loop (Repeat Until Condition Fails)

count = 0

while count < 5:
    print("Count:", count)
    count += 1

Output:

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

✅ Use Case: Keeping a server running, waiting for a user input, or training an ML model until convergence.

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🔹 4.3 Loop Control Statements

Python provides ways to modify loop behavior using break, continue, and pass.

🔹 break (Exit Loop Early)

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

Output:

0
1
2
3
4

✅ Use Case: Stopping an AI model early if a condition is met.

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🔹 continue (Skip Iteration)

for num in range(5):
    if num == 2:
        continue  # Skips 2
    print(num)

Output:

0
1
3
4

✅ Use Case: Skipping invalid data points in datasets.

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🔹 pass (Do Nothing)

for i in range(5):
    if i == 3:
        pass  # Placeholder
    print(i)

✅ Use Case: Placeholder for functions, classes, loops.

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🔹 4.4 List Comprehensions for Loops

Python supports one-liner loops with list comprehensions, improving efficiency.

numbers = [x * 2 for x in range(5)]
print(numbers)

Output: [0, 2, 4, 6, 8]

✅ Use Case: Feature engineering, transforming datasets, list filtering.

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🔹 4.5 Exception Handling (try-except-finally)

Handling exceptions prevents crashes in programs.

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")
finally:
    print("Execution complete.")

Output:

Cannot divide by zero!
Execution complete.

✅ Use Case: Preventing failures in data pipelines, ML model training.

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🚀 Summary

Concept	Key Takeaway
if-elif-else	Executes different blocks based on conditions
for loop	Iterates over sequences (lists, tuples, etc.)
while loop	Runs while condition is True
break	Exits loop early
continue	Skips current iteration
pass	Placeholder statement
List Comprehensions	Shorter syntax for loops
Exception Handling	Prevents program crashes

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🔚 Final Thoughts

Control flow is crucial for decision-making and iteration in Python. Mastering it allows writing efficient, error-free code.

Would you like exercises or real-world examples to reinforce these topics? 🚀