loops

for and for else loop

• In Python, for loops provide a concise way to iterate over sequences (like lists, tuples, or strings) and execute a block of code for each item in the sequence. Additionally, for loops can have an optional else clause that executes only if the loop completes normally (without encountering a break statement).

# Basic for Loop
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# Basic for Loop fruits = ["apple", "banana", "cherry"] for fruit in fruits: print(fruit)

• This loop iterates over the fruits list.
• In each iteration, the variable fruit takes on the value of the current item in the list ("apple", "banana", "cherry" in this case).
• The indented code block (printing the fruit name) is executed for each item.

# Looping with Index
numbers = [1, 2, 3, 4]
for index, number in enumerate(numbers):
    print(f"Index: {index}, Number: {number}")

# Looping with Index numbers = [1, 2, 3, 4] for index, number in enumerate(numbers): print(f"Index: {index}, Number: {number}")

• This example uses enumerate(numbers) to get both the index (position) and the value in each iteration.
• index takes on the index of the current item, while number holds the actual value.

# Looping over a Range
for i in range(5):  # Range from 0 (inclusive) to 5 (exclusive)
    print(i)

# Looping over a Range for i in range(5): # Range from 0 (inclusive) to 5 (exclusive) print(i)

• The range(n) function generates a sequence of numbers from 0 (inclusive) to n-1 (exclusive).
• This loop iterates 5 times, printing each number from 0 to 4.

# for-else Loop
found = False
for number in range(10):
    if number == 5:
        found = True
        break
if found:
    print("Number 5 found in the list!")
else:
    print("Number 5 not found.")

# for-else Loop found = False for number in range(10): if number == 5: found = True break if found: print("Number 5 found in the list!") else: print("Number 5 not found.")

• The else clause is optional and only executes if the loop completes normally (without break).
• In this example, if number is 5, found becomes True, and the loop breaks using break.
• Since the loop didn't complete normally, the else block doesn't execute.
• If number never reaches 5, the loop finishes iterating, and the else block prints that 5 wasn't found.
• Key Points
  • Use for loops to efficiently iterate over sequences and process items one by one.
  • You can optionally include an index along with the item in each iteration.
  • range(n) is useful for iterating a specific number of times.
  • The else clause provides a way to execute code only when the loop completes normally (no break).

while loop

• A while loop in Python is a control flow statement that repeatedly executes a block of code as long as a certain condition is true.

  while condition:
      # code to be executed while the condition is true
  

• while keyword
  • This keyword marks the beginning of the while loop.
• condition
  • This is a Boolean expression that determines whether the loop continues to execute.
  • The loop keeps running as long as the condition evaluates to True. Once the condition becomes False, the loop terminates.
  • Indented block
    • The code you want to execute repeatedly goes here.
    • The indentation level defines the code block that belongs to the loop.
    • Make sure all the code you want to repeat is indented at the same level.
• Common Uses of While Loops
  • Iterating a specific number of times (using a counter variable).
  • Reading user input until a specific condition is met (e.g., entering a valid value).
  • Processing data from a file line by line as long as there's more data to read.
  • Simulating games or other interactive applications where the loop continues until a specific event occurs (e.g., winning or losing a game).

count = 0
while count < 5:
  print("Count:", count)
  count += 1  # Increment count by 1

count = 0 while count < 5: print("Count:", count) count += 1 # Increment count by 1

• Explanation
  • The loop variable count is initialized to 0.
  • The while condition checks if count is less than 5 (count < 5).
  • As long as the condition is True (initially and until count reaches 4), the indented code block executes.
  • Inside the block, count is printed, and then incremented by 1 using count += 1.
  • After each iteration, the condition is checked again. Once count becomes 5, the condition becomes False, and the loop terminates.

break, continue, pass

• These three (break, continue, and pass) are control flow statements that influence the execution flow within loops (and conditionally in the case of pass) in Python.
• break: The break statement abruptly terminates the loop it's within, regardless of the loop condition's state (even if it's still True). Control jumps to the statement following the loop's complete execution
  • Below code iterates from 0 to 9, but upon reaching 5, the break statement exits the loop, printing only numbers 0 to 4.

for number in range(10):
    if number == 5:
        print("Found 5, breaking out of the loop!")
        break
    print(number)

for number in range(10): if number == 5: print("Found 5, breaking out of the loop!") break print(number)

• continue: The continue statement skips the current iteration of the loop and immediately jumps to the beginning of the next iteration. The remaining code within the current iteration is not executed.
  • Below code loop iterates from 0 to 9. The continue statement skips even numbers, resulting in only odd numbers being printed (1, 3, 5, 7, 9).

for number in range(10):
    if number % 2 == 0:  # Skip even numbers
        continue
    print(number)

for number in range(10): if number % 2 == 0: # Skip even numbers continue print(number)

• pass: The pass statement acts as a placeholder, essentially doing nothing. It's used syntactically when a statement is required but you don't want any action to occur at that point.
  • Below code pass fills the empty block, allowing the loop to function correctly without any action within the loop itself.

for number in range(5):
    pass  # Placeholder, no action
print("Loop finished!")

for number in range(5): pass # Placeholder, no action print("Loop finished!")

• Points to remember
  • break exits the entire loop.
  • continue skips the current iteration and moves to the next.
  • pass is a null statement, acting as a placeholder.
  • These statements are most commonly used within loops, but pass can also be used in conditional statements (like if statements) in specific situations.