Python program to print all prime numbers in a range

In this tutorial we will write a Python program to print all prime numbers in a range . Before reading further we recommend to read about below tutorial-

• If-Else Statement in Python
• Python For Loop
• Break statement in Python

What is Prime number

A positive integer number which is greater than 1 and only divisible by 1 and that number is called Prime number .

Example :

• 2 is a prime number as 2 is only divisible by 1 and 3 .
• 3 is a prime number as 3 is only divisible by 1 and 3.
• 4 is not a prime number because it is not only divisible by 1 and 4 , it is also divisible by 2 .

Python program to print all prime numbers in a range

Steps:

• First we will define a is_prime() function which will take a number as function argument and return True if the given number is a prime number else return False . To know more about is_prime() function click here .
• After that we will define a function named prime_numbers() which will take two numbers as range(start-end) . This function will print all the prime numbers in the given range .
• If the value of end parameter is less than 2 then we simply return None . Because value of lowest prime number is 2
• If the value of start parameter is less than 2 and value of end parameter is greater than 1 so we simply change the value of start parameter as 2 . Because no of prime numbers in range -10 to 10 is equal to no of prime numbers in range 2 to 10 .
• After that we will iterate every number from start to end and print the number if the number is a prime number .

import math

# defining a function to check 
# if a given number is prime or not
def is_prime(number):
    # declaring a flag variable 
    prime=True
    # trying to divide the number by the numbers 
    # starting from 2
    for i in range(2,int(math.sqrt(number)+1)):
        if number%i==0:
            # if the number is divisable by any number
            # staring from 2 then change the flag variable
            # and exit immediately from the loop
            prime=False
            break
    return prime

# define a function to print
# all prime numbers in a range
def prime_numbers(start,end):
    # if end is less than 2 we simply return none
    # and exit from the function
    if end<2:
        return None
    else:
        # if start is less than 2 and end is greater than 1
        # so change the value of start as 2
        if (start<2 and end>1):
            start=2
        # traversing every number from start to end
        # and print the number if the number is prime number
        for i in range(start,end+1):
            if is_prime(i)==True:
                print(i,end=" ")   
        print()


# calling the function
prime_numbers(-2,0)
prime_numbers(-2,5)
prime_numbers(4,10)

2 3 5 
5 7

• In the above code we have written a function named prime_numbers() which will print all the prime numbers in a range .
• As there is no prime number in between -2 and 0 so prime_numbers(-2,0) did not print anything .
• prime_numbers(-2,5) line is printed 2 3 5 in the output as in between -2 to 5 there are only three prime numbers 2 , 3 ,5 .
• prime_numbers(4,10) line is printed 5 7 in the output as in between 4 to 10 there are only two prime numbers 5 , 7 .

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