"""Prime Numbers, by Al Sweigart al@inventwithpython.com
Calculates prime numbers, which are numbers that are only evenly
divisible by one and themselves. They are used in a variety of practical
applications.
More info at: https://en.wikipedia.org/wiki/Prime_number
This code is available at https://nostarch.com/big-book-small-python-programming
Tags: tiny, math, scrolling"""
import math, sys
def main():
print('Prime Numbers, by Al Sweigart al@inventwithpython.com')
print('Prime numbers are numbers that are only evenly divisible by')
print('one and themselves. They are used in a variety of practical')
print('applications, but cannot be predicted. They must be')
print('calculated one at a time.')
print()
while True:
print('Enter a number to start searching for primes from:')
print('(Try 0 or 1000000000000 (12 zeros) or another number.)')
response = input('> ')
if response.isdecimal():
num = int(response)
break
input('Press Ctrl-C at any time to quit. Press Enter to begin...')
while True:
# Print out any prime numbers:
if isPrime(num):
print(str(num) + ', ', end='', flush=True)
num = num + 1 # Go to the next number.
def isPrime(number):
"""Returns True if number is prime, otherwise returns False."""
# Handle special cases:
if number < 2:
return False
elif number == 2:
return True
# Try to evenly divide number by all numbers from 2 up to number's
# square root.
for i in range(2, int(math.sqrt(number)) + 1):
if number % i == 0:
return False
return True
# If this program was run (instead of imported), run the game:
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
sys.exit() # When Ctrl-C is pressed, end the program.