Python for Beginners -part 2
Looping with While Loops in Python
Introduction
While loops are used in Python to repeatedly execute a block of code as long as a certain condition is
true. This is different from a for loop, which iterates over a sequence (like a list or string) a specific
number of times.
While Loop Syntax
The basic syntax for a while loop is as follows:
while condition:
# code to be executed as long as condition is true
It is important to ensure that the condition will eventually become False, otherwise the loop will
continue indefinitely. This is known as an infinite loop and should be avoided.
Example:
Here's an example of using a while loop to print the numbers 1-5:
count = 1
while count <= 5:
print(count)
count += 1
This loop continues to execute as long as the variable count is less than or equal to 5. Each time
through the loop, it prints the current value of count and then increments it by 1.
Getting User Input and Performing Basic Calculations
While loops can also be used in conjunction with the input() function to get input from the user and
perform calculations based on that input.
Example:
Here's an example of getting a number from the user and printing whether it is even or odd:
num = int(input("Enter a number: "))
while num != 0:
if num % 2 == 0:
print("Even")
else:
print("Odd")
num = int(input("Enter a number: "))
, In this example, the loop continues to execute as long as the user enters a number that is not zero. If
the number is even, it prints "Even". If the number is odd, it prints "Odd".
Checking for Existence of Items in Lists with the In Operator
The in operator can be used in a while loop to check for the existence of an item in a list.
Example:
Here's an example of using the in operator to find the first prime number in a list:
numbers = [4, 5, 6, 7, 8]
i=0
while i < len(numbers):
if numbers[i] > 1:
is_prime = True
j=2
while j < numbers[i]:
if numbers[i] % j == 0:
is_prime = False
break
j += 1
if is_prime:
print(numbers[i])
break
i += 1
In this example, the loop iterates over each number in the list. If the number is greater than 1, it
checks if it is prime by dividing it by all numbers less than itself. If it is prime, it prints the number and
breaks out of the loop.
Conclusion
While loops are a powerful tool in Python that allow you to repeatedly execute a block of code as
long as a certain condition is true. They can be used for a variety of tasks, including getting user
input, performing calculations, and iterating over lists. It is important to ensure that the condition
will eventually become False and to use the break statement to exit the loop when necessary.
Here are the notes on the topic "Working with Lists in Python":
Working with Lists in Python
Lists are one of the fundamental data structures in Python. They are ordered collections of items,
which can be of different data types. Lists are written with square brackets [ ]. Here are some of the
main methods and operations that can be performed on lists in Python.
Looping with While Loops in Python
Introduction
While loops are used in Python to repeatedly execute a block of code as long as a certain condition is
true. This is different from a for loop, which iterates over a sequence (like a list or string) a specific
number of times.
While Loop Syntax
The basic syntax for a while loop is as follows:
while condition:
# code to be executed as long as condition is true
It is important to ensure that the condition will eventually become False, otherwise the loop will
continue indefinitely. This is known as an infinite loop and should be avoided.
Example:
Here's an example of using a while loop to print the numbers 1-5:
count = 1
while count <= 5:
print(count)
count += 1
This loop continues to execute as long as the variable count is less than or equal to 5. Each time
through the loop, it prints the current value of count and then increments it by 1.
Getting User Input and Performing Basic Calculations
While loops can also be used in conjunction with the input() function to get input from the user and
perform calculations based on that input.
Example:
Here's an example of getting a number from the user and printing whether it is even or odd:
num = int(input("Enter a number: "))
while num != 0:
if num % 2 == 0:
print("Even")
else:
print("Odd")
num = int(input("Enter a number: "))
, In this example, the loop continues to execute as long as the user enters a number that is not zero. If
the number is even, it prints "Even". If the number is odd, it prints "Odd".
Checking for Existence of Items in Lists with the In Operator
The in operator can be used in a while loop to check for the existence of an item in a list.
Example:
Here's an example of using the in operator to find the first prime number in a list:
numbers = [4, 5, 6, 7, 8]
i=0
while i < len(numbers):
if numbers[i] > 1:
is_prime = True
j=2
while j < numbers[i]:
if numbers[i] % j == 0:
is_prime = False
break
j += 1
if is_prime:
print(numbers[i])
break
i += 1
In this example, the loop iterates over each number in the list. If the number is greater than 1, it
checks if it is prime by dividing it by all numbers less than itself. If it is prime, it prints the number and
breaks out of the loop.
Conclusion
While loops are a powerful tool in Python that allow you to repeatedly execute a block of code as
long as a certain condition is true. They can be used for a variety of tasks, including getting user
input, performing calculations, and iterating over lists. It is important to ensure that the condition
will eventually become False and to use the break statement to exit the loop when necessary.
Here are the notes on the topic "Working with Lists in Python":
Working with Lists in Python
Lists are one of the fundamental data structures in Python. They are ordered collections of items,
which can be of different data types. Lists are written with square brackets [ ]. Here are some of the
main methods and operations that can be performed on lists in Python.
