Python - Loops
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In Python, a loop is a programming construct that allows the execution of a sequence of statements or a block of code repeatedly. There are two main types of loops in Python: for loop and while loop. Let's discuss each with examples.
1. for Loop:
# Example of a for loop
numbers = [1, 2, 3, 4, 5]
for num in numbers:
print(num)
1 2 3 4 5
In this example, the for loop iterates over each element in the numbers list, and the variable num takes on each value in the list during each iteration. The print statement prints each value.
2. while Loop:
# Example of a while loop
counter = 0
while counter < 5:
print(counter)
counter += 1
0 1 2 3 4
In this example, the while loop continues to execute the block of code as long as the condition counter < 5 is true. The print statement prints the value of counter, and counter += 1 increments the counter in each iteration.
Loops are essential for tasks that require repetitive execution, such as iterating through elements in a list, processing data until a certain condition is met, or implementing controlled repetition.
for and while loops in Python.
In Python, both for and while loops are used for repetitive execution of a block of code. However, they have key differences in terms of syntax and use cases.
for loops are used when the number of iterations is known beforehand, such as when iterating over elements in a list or any iterable object. The loop variable takes on each value in the sequence during each iteration.
while loops are used when the number of iterations is not known beforehand, and the loop continues as long as a certain condition is true. The loop variable is typically initialized before the loop, and the condition is checked before each iteration.
Let's explore another example to illustrate the differences between for and while loops. This time, we'll use them to calculate the factorial of a number.
Using a for loop:
def factorial_with_for_loop(n):
result = 1
for i in range(1, n + 1):
result *= i
return result
# Example: Calculate factorial of 5
result_for = factorial_with_for_loop(5)
print(result_for)
Output:
120
Using a while loop:
def factorial_with_while_loop(n):
result = 1
counter = 1
while counter <= n:
result *= counter
counter += 1
return result
# Example: Calculate factorial of 5
result_while = factorial_with_while_loop(5)
print(result_while)
Output:
120
In summary, for loops are suitable when the number of iterations is known, and while loops are suitable when the loop should continue until a specific condition is met.
for loop to iterate over a sequence in Python?
In Python, the for loop is commonly used to iterate over a sequence. Let's consider an example where we use a for loop to iterate over a list of numbers and print each element.
# Example: Using a for loop to iterate over a list
numbers = [1, 2, 3, 4, 5]
print("Iterating over the list using a for loop:")
for num in numbers:
print(num)
Output:
Iterating over the list using a for loop: 1 2 3 4 5
In this example, the for loop iterates over each element in the list numbers, and the variable num takes the value of each element in each iteration.
range() function in a for loop?
The range() function in Python is often used in for loops to generate a sequence of numbers. It helps in iterating a specific number of times or creating a sequence of numbers without explicitly specifying all the values.
Let's explore an example where we use range() in a for loop to print the numbers from 0 to 4.
# Example: Using range() in a for loop
print("Printing numbers from 0 to 4 using range():")
for num in range(5):
print(num)
Output:
Printing numbers from 0 to 4 using range(): 0 1 2 3 4
In this example, range(5) generates a sequence of numbers from 0 to 4. The for loop iterates over this sequence, and the variable num takes each value in each iteration.
The range() function is flexible and can take different arguments to customize the sequence it generates. Let's look at an example where we use range() with start, end, and step arguments in a for loop.
# Example: Using range() with start, end, and step in a for loop
print("Printing even numbers from 2 to 10 using range():")
for even_num in range(2, 11, 2):
print(even_num)
Output:
Printing even numbers from 2 to 10 using range(): 2 4 6 8 10
In this example, range(2, 11, 2) generates a sequence of even numbers starting from 2, up to (but not including) 11, with a step of 2. The for loop iterates over this sequence, and the variable even_num takes each value in each iteration.