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1. What are Loops?

  • Loops are used to repeatedly execute a block of code.
  • They are essential for automating repetitive tasks and iterating over sequences like lists, tuples, strings, etc.
  • Python supports two types of loops:
    1. for loops
    2. while loops

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2. for Loop

  • The for loop is used to iterate over a sequence (e.g., list, tuple, string, range) or other iterable objects.
  • Syntax: 
    for item in sequence:
    # Code to execute

Example:

names = ["Raj", "Ram", "Anand", "Bala"]
for name in names:
    print(f"Hello, {name}!")

Output:

Hello, Raj!
Hello, Ram!
Hello, Anand!
Hello, Bala!

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Using range() in for Loops

  • The range() function generates a sequence of numbers.
  • It is commonly used to iterate a specific number of times.

Example:

for i in range(5):  # Iterates from 0 to 4
    print(i)

Output:

0
1
2
3
4

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3. while Loop

  • The while loop repeats a block of code as long as a condition is True.
  • Syntax: 
    while condition:
    # Code to execute

Example:

count = 0
while count < 5:
    print(f"Count: {count}")
    count += 1

Output:

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

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4. Loop Control Statements

  • These statements alter the flow of loops:
    1. break: Exits the loop immediately.
    2. continue: Skips the rest of the code in the current iteration and moves to the next iteration.
    3. pass: A placeholder for future code (does nothing).

Examples:

  • break:

    for i in range(10):
    if i == 5:
        break  # Exit the loop when i is 5
    print(i)

    Output:

    0
1
2
3
4

  • continue:

    for i in range(5):
    if i == 2:
        continue  # Skip the rest of the code for i = 2
    print(i)

    Output:

    0
1
3
4

  • pass:

    for i in range(3):
    if i == 1:
        pass  # Placeholder for future code
    print(i)

    Output:

    0
1
2

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5. Nested Loops

  • A loop inside another loop is called a nested loop.
  • Commonly used for working with multi-dimensional data structures.

Example:

for i in range(3):  # Outer loop
    for j in range(2):  # Inner loop
        print(f"i={i}, j={j}")

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

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6. Iterating Over Sequences

  • Loops can iterate over various sequences like lists, tuples, strings, dictionaries, etc.

Examples:

  • List:

    numbers = [10, 20, 30, 40]
for num in numbers:
    print(num)

  • String:

    name = "Karthik"
for char in name:
    print(char)

  • Dictionary:

    person = {"name": "Kumar", "age": 25, "city": "Chennai"}
for key, value in person.items():
    print(f"{key}: {value}")

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7. Additional Examples

  • for Loop:

    names = ["Siva", "Ramesh", "Suresh", "Sathish"]
for name in names:
    print(f"Welcome, {name}!")

  • while Loop:

    count = 1
while count <= 3:
    print(f"Attempt {count}")
    count += 1

  • Nested Loops:

    for i in range(2):  # Outer loop
    for j in range(3):  # Inner loop
        print(f"i={i}, j={j}")

  • Loop Control:

    for i in range(10):
    if i == 7:
        break  # Exit the loop when i is 7
    print(i)

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8. Best Practices

  • Use meaningful variable names for iterators (e.g., name instead of x).
  • Avoid infinite loops in while loops by ensuring the condition eventually becomes False.
  • Use break and continue sparingly to keep the code readable.
  • Use list comprehensions for simple loops that create lists.

Example:

squares = [x ** 2 for x in range(5)]  # List comprehension
print(squares)  # Output: [0, 1, 4, 9, 16]