For Loop in Python

In Python, a for loop is used to iterate over a sequence (that can be a list, tuple, dictionary, string, set, range etc.) and perform the same action on each element in the sequence. The for loop is an essential tool for any Python programmer.

Syntax

The syntax of a for loop in Python is as follows:

for var in sequence:
    # code block to be executed for each value of var

Here, var is the variable that takes on the value of each element in the sequence, one at a time. The sequence can be any iterable object in Python.

Example

# Print all the numbers from 0 to 9
for i in range(10):
    print(i)

Output:

0
1
2
3
4
5
6
7
8
9

In this example, range(10) returns a sequence of numbers from 0 to 9, and the for loop iterates over each value of i in the sequence and prints it to the console.

Nested Loops

In Python, it is possible to nest one for loop inside another. This is useful when working with two-dimensional arrays or matrices, or when we want to perform an action on each element in a list of lists.

# Print all the elements in a 2D array
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

for row in matrix:
    for item in row:
        print(item)

Output:

1
2
3
4
5
6
7
8
9

In this example, we have a 2D array of integers called matrix. We use two nested for loops to iterate over each element in the matrix and print it to the console.

Conclusion

The for loop is a powerful tool in Python, and it is essential for any programmer to understand its syntax and usage. With the for loop, we can iterate over sequences of elements and perform the same action on each element. We can also nest for loops to work with two-dimensional arrays or perform more complex operations.