5.2 For loop

For loops are powerful tools in Python, allowing you to iterate through sequences like lists, strings, and ranges. They simplify repetitive tasks by executing a block of code for each item in a sequence, making your programs more efficient and readable.

The range() function works hand-in-hand with for loops, generating number sequences for iteration. For loops are versatile, working with various data types and performing tasks like calculations, finding values, and modifying elements based on conditions.

Iteration with for loops

Implement a for loop to iterate through a sequence of elements

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• For loops enable iterating over a sequence of elements (lists, tuples, strings, or other iterable objects)
• For loop syntax:

  for variable in sequence:

  • variable

    (also known as the loop variable) takes on each value in the

    sequence

    one at a time
  • Code block under the for loop (loop body) executes for each value of

    variable

• Iterating over a list example:

  fruits = ['apple', 'banana', 'cherry']
  for fruit in fruits:
      print(fruit)
  

  Output:

  apple
  banana
  cherry
  

Range function for sequences

• range()

  function generates a sequence of numbers
  • Syntax:

    range(start, stop, step)

    • start

      : Starting number of the sequence (inclusive, default 0)

    • stop

      : Ending number of the sequence (exclusive)

    • step

      : Increment between each number (default 1)

• range()

  examples:

  • range(5)

    : Generates numbers 0 to 4 (0, 1, 2, 3, 4)

  • range(1, 6)

    : Generates numbers 1 to 5 (1, 2, 3, 4, 5)

  • range(1, 10, 2)

    : Generates odd numbers 1 to 9 (1, 3, 5, 7, 9)
• Using

  range()

  with for loops:

  for i in range(5):
      print(i)
  

  Output:

  0
  1
  2
  3
  4
  

For loops across data types

• For loops work with various data types:
  • Lists:

    numbers = [1, 2, 3, 4, 5]
    for num in numbers:
        print(num ** 2)
    

    Output: 1, 4, 9, 16, 25
  • Strings:

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

    Output: J, o, h, n
  • Dictionaries (iterating over keys):

    person = {"name": "Alice", "age": 25, "city": "New York"}
    for key in person:
        print(key)
    

    Output: name, age, city
• For loops perform repetitive tasks:
  1. Calculating sum or product of a list of numbers
  2. Finding maximum or minimum value in a list
  3. Counting occurrences of specific elements in a list
  4. Modifying elements in a list based on conditions

Loop Control Flow and Structure

• Loop control flow determines how the program executes the loop
• The iterator is the object that produces the next item in the sequence
• Proper indentation is crucial for defining the loop body and maintaining correct execution
• The sequence is the iterable object being looped over (e.g., list, string, or range)