Python Loops: Basics and Examples

Python Loops: Basics and Examples

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Akshobya KL
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3 min read

Loops in Python

While Loop

  • A while loop in Python repeats a block of code as long as a specified condition remains True.

  • It is ideal when we don’t know beforehand how many times we want to execute a block of code, but want to keep running it as long as a condition holds.

  • while condition: # Code

  • Condition: The loop continues as long as the condition is True. Once it becomes False, the loop stops.

  • Indentation the body of the loop must be indented to indicate which code is inside the loop.

Breaking out of a loop:

  • We can use the break statement to exit a while loop before the condition becomes False (for example, when we meet a specific condition within the loop).

  • else with while: Python allows an optional else block with while. It runs only if the loop wasn’t exited with break.

For Loop

  • A for loop is used to iterate over a sequence and perform an action for each item.

  • It’s used when we know exactly how many iterations we need to work with.

  • for item in sequence:

  • Sequence: This can be any iterable object (list, string, etc). The loop will go through each item in the sequence.

  • Item: During each iteration, the item variable holds the current value from the sequence.

  • Indentation: The code block inside the for loop must be indented to indicate it belongs to the loop.

  •       my_list= [1, 2, 3, 5]
      print(my_list[0])
      my_list.append("april")
      print(my_list[4])

  • range() function:

    • A common use of the for loop is with the range() function, which generates a sequence of numbers.

  • Similar to while, we can use the break statement to stop the loop early.

  • Below are the example loops used in our main example


calc_of_units = 24
name_of_units = "hours"


def days_to_units(num_of_days):

        return f"{num_of_days} days are {num_of_days * calc_of_units} {name_of_units}"


def validate_exe():
    try:

        user_inp_num = int(num_of_days_elem)
        if user_inp_num > 0 :
             calc_value = days_to_units(user_inp_num)
             print(calc_value)
        elif user_inp_num == 0:
             print("you entered 0")
        else:
             print("negative num")
    except ValueError: 
        print("not a valid num")
user_inp = " "
while user_inp != "exit": 
     user_inp = input("input no of days i will convert it to hours\n")
     for num_of_days_elem in user_inp.split(", "):
          validate_exe()

Comments

Comments improve the readability and maintainability of code.

Single-line comments:

  • Start with a # symbol and continue until the end of the line.

  • These comments are used for brief explanations.

Multi-line comments:

  • we use triple quotes (''' or """) to create block comments

  • Triple quotes can span multiple lines, but technically these are treated as docstrings (often used for documentation rather than commenting out code).

Python