17 - For Loops

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2023-12-17 - 18:22

Sometimes a programmer wants to execute a group of statements a certain number of times. This can be done using loops. Based on this, loops are further classified into following main types;

The for loop

for loops can iterate over a sequence of iterable objects in python. Iterating over a sequence is nothing but iterating over strings, lists, tuples, sets and dictionaries.

Example: iterating over a string:

name = 'Abhishek'
for i in name:
	print(i, end=", ")

Output:

A, b, h, i, s, h, e, k,

Example: iterating over a list:

colors = ["Red", "Green", "Blue", "Yellow"]
for x in colors:
	print(x)

Output:

Red
Green
Blue
Yellow

Similarly, we can use loops for lists, sets and dictionaries.

range():

What if we do not want to iterate over a sequence? What if we want to use for loop for a specific number of times?

Range has 3 parameters: Start, Stop, and Step.

Start

Is from where the numbers start. If you add for K in range(0, 5). The range will start from 0.

Stop

Is where the number stops. If you add for K in range(0,5). The range will stop at 4. Yes! 4 not 5. It always stops at a number before what you entered. As the number you entered will not be added to the list.

Step

Is the number of steps it skips. If you add for K in range(0,10,2). You will see 0,2,4,6,8 same as stop it will never print 10 as we've told the program to stop at it reaches 10.

Here, we can use the range() function.

Example:

for k in range(5):
	print(k)

Output:

0
1
2
3
4
Here, we can see that the loop starts from 0 by default and increments at each iteration.

But we can also loop over a specific range.

Example:

for k in range(4,9):
	print(k)

Output:

4
5
6
7
8

Quick Quiz

Explore about third parameter of range (ie range(x, y, z))

Example:

for k in range(1, 12, 3):
	print(k)