Control Flow

Control statements are vital in programming as they allow you to control the flow of execution in your code. In Python, several control statements help you make decisions, loop through code blocks, and handle exceptions.

Conditional Statement(if, elif, else)

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

The most common conditional statement in Python is the if statement.

  age = 25

  if age < 18:
      print("You are underage.")
  elif age >= 18 and age < 60:
      print("You are an adult.")
  else:
      print("You are a senior citizen.")

In the above example, the program checks the value of the age variable and prints the corresponding message based on the condition.

Match and Switch Statement : python 3.10+

From version python 3.10+, Python has implemented a switch case feature called “structural pattern matching”.


  number  = int(input("Enter day  ::"))
  match number:
      case 1:
          return "Sunday"
      case 2:
          return "Monday"
      case 3:
          return "Tuesday"
      case 4:
          return "Wednesday"
      case 5:
          return "Thursday"
      case 6:
          return "Friday"
      case 7:
          return "Saturday"
      case _:
          return "Week has only 7 days"

Looping Statements (for, while)

Looping statements enable you to execute a block of code repeatedly. Python offers two types of looping statements: for loop and while loop. Let's take a look at examples of both:

for loop example:

  list = [1,2,3]
  for i in list:
      print(i,end = " ")
  #Output = 1 2 3

For loop using range(start, stop, step) method.

start (optional): The starting value of the sequence (inclusive). If not specified, it defaults to 0.
stop (required): The ending value of the sequence (exclusive). The range() function will generate numbers up to but excluding this value.

step (optional): The difference between each number in the sequence. If not specified, it defaults to 1.

  list = list(range(1, 6))
  print(my_list)
  # Output: [1, 2, 3, 4, 5]

  for i in range(6):
      print(i,end = " ")
  #output = 0, 1, 2, 3, 4, 5(this exclude 6)

  for i in range(1,6):
      print(i,end = " ")
  #output = 1, 2, 3, 4, 5

  '''Reverse number'''
  '''In this statement starts from 5 to (0+1).Here, -1 is for reverse'''
  for i in range(5,0,-1):
      print(i,end = " ")
  #Output = 5, 4, 3, 2, 1

while loop example:

  count = 0
  while count < 10:
      print("Count:", count)
      count += 1

Here, the while loop continues executing the code block until the condition count < 10 becomes False.

Break and Continue statements

Python provides control statements to alter the flow of loops. Two commonly used control statements are break and continue. Let's see them in action:

break statement example:

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    if fruit == "banana":
        break
    print(fruit)

In this example, the break statement is used to terminate the loop prematurely when the value of fruit is "banana". The loop exits at that point.

continue statement example:

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

for num in numbers:
    if num % 2 == 0:
        continue
    print(num)

Here, the continue statement skips the remaining code in the loop for even numbers. It moves on to the next iteration and prints only the odd numbers.

Looping statement with else block

The loop-else statement in Python is often confusingly named.
An alternative way to understand it is as a nobreak statement. This means that the else block is executed only if the loop completes naturally without encountering a "break" statement.

Take into account the following implementation of the Sieve of Eratosthenes. This algorithm is widely recognized for its ability to find prime numbers.

'''Prime number from 1 to 20'''
list = []
number = 20
for n in range(2, number):
    for factor in list:
        if n % factor == 0:
        break
    else: # no break
        list.append(n)    
print(list)#output = [2, 3, 5, 7, 11, 13, 17, 19]