Python Data Persistence - Using range

Python Data Persistence – Using range

Python’s built-in range ( ) function returns an immutable sequence of numbers that can be iterated over by for loop. The sequence generated by the range ( ) function depends on three parameters.

The start and step parameters are optional. If it is not used, then the start is always 0 and the step is 1. The range contains numbers between start and stop-1, separated by a step. Consider an example 2.15:

Example

range (10) generates 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9

range ( 1 , 5 ) results in 1 , 2 , 3 , 4

range ( 20 , 30 , 2 ) returns 20 , 22 , 24 , 26 , 28

We can use this range object as iterable as in example 2.16. It displays squares of all odd numbers between 11-20. Remember that the last number in the range is one less than the stop parameter (and step is 1 by default)

Example

#for-3.py
for num in range( 11 , 21 , 2 ):
sqr=num*num
print ( ' sqaure of { } is { } ' . format( num , sqr ) )

Output:

E:\python37>python for-3.py 
square of 11 is 121 
square of 13 is 169 
square of 15 is 225 
square of 17 is 289 
square of 19 is 361

In the previous chapter, you have used len ( ) function that returns a number of items in a sequence object. In the next example, we use len ( ) to construct a range of indices of items in a list. We traverse the list with the help of the index.

Example

#for-4.py
numbers=[ 4 , 7 , 2 , 5 , 8 ]
for indx in range(len(numbers)):
sqr=numbers[indx]*numbers[indx]
print ( ' sqaure of { } is { } ' . format ( numbers [ indx ] , sqr ) )

Output:

E:\python3 7 >python for - 4.py 
sqaure of 4 is 16 
sqaure of 7 is 49 
sqaure of 2 is 4 
sqaure of 5 is 25 
sqaure of 8 is 64 

E:\python37>

Have a look at another example of employing for loop over a range. The following script calculates the factorial value of a number. Note that the factorial of n (mathematical notation is n!) is the cumulative product of all integers between the range of 1 to n.

Example

#factorial.py
n=int ( input ( " enter number . . " ) )
#calculating factorial of n
f = 1
for i in range ( 1 , n+1 ):
f = f * i
print ( ' factorial of { } = { } ' . format ( n , f ) )

Output:

E:\python37>python factorial.py 
enter number..5 
factorial of 5 = 120

Python Data Persistence – Using range

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