Python range Function in for loop

Python range Function in for loop – this python tutorial will explain the purpose and use of Python range() function especially in for loop.

The Use of Python range Function in for loop

The range function

The range() function creates the sequence of numbers for you. When using the range() function, you specify the start, stop and step values.

Syntax of  range() function is

range(start(inclusive), stop(excluded),step)

start value gives the starting number (inclusive)of the sequence.

stop value gives ending value exclusive

step is the increment if positive number or decrement if negative number.

Example:

range(1,11,1) will produce a sequence of numbers from 1 to 10. since start is 1, and stop value is 11 wihich is excluded. The step or increment is of one, so the result is 1,2,3,4,5,6,7,8,9,10.

Here the default value of start is 0 and of step is 1. Hence if we donot use start value it is zero by default. And if we do not use a step value, the default value is a 1.

Example:

range(1,6) will give 1,2,3,4,5 stop value 6 will not be included.

range(6) will give 0,1,2,3,4,5 stop value 6 is not included.

 

Normally, we use range() function in for loop statemt to execute a block of statements for a specified number of times.
The argument value we use in the range function decides  how many times the loop will execute.

Why we use range function?

Actually the range function generates a list of numbers from start(by default start is zero)  to the last value minus one. For instance, range(10) is equal to range(0,10). Therefore, range(10)
produces ten values: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. The last value minus one means, excluding the value itself. For example, the range(3) will give 0,1 and 2. It will exclude the number 3.

First and Last Value of range function

The range() function by default uses 0(zero) as the first value and value minus one as the last value produced. For example, range(5) will give total five values but from zero to 4. Here first value is by default zero and last value is the value minus one so 5-1 = 4.

The Syntax of range function in Python

range(start,last_minus_one,step)

Where:

• start is the first or starting number in the range. By default it is zero.

Example:
range(3) will give 0,1,2
range(1,3) will give 1,2
range(1,6) will give 1,2,3,4,5
so we will use start=1 and last=six, if we wish to produce a range of 1 to 5 numbers.

• last_minus_one represents the value before last. For example, if we use the range(5), it will produce 0, 1, 2, 3, 4. It will not give tha last value. It will generate total 5 values but from 0 to 4.

Examples:
range(4) will give 0,1,2,3
range(1,5) will give 1,2,3,4

• The third argument is step. It represents the increment or decrement in starting value each time for producing the new number. It is an optional argument. By default its value is 1. Therefore if we ignore it, the step will be 1.

Examples:
range(1,5,1) will give 1,2,3,4
range(1,7,2) will give 2,4,6 note the increment of 2

How to use range() function to display 10 down to 1

we use starting value as 10, last value as 0( zero) and step will be -1.

Hence range(10,0,-1) will produce 10,9,8,7,6,5,4,3,2,1. Zero will be excluded.

Write down a Python for statement with range function to show 10 down to 1 (first 10 numbers in reverse)

for i in range(10,0,-1):
    print(i)

will give the output:
10
9
8
7
6
5
4
3
2
1

Because, starting value is 10 and stop value is a zero 
and step value is 1.
It will display 10 down to 1 because stop value zero is
excluded.