Prime number(Python 3)

Question

My goal is to build a programm, that says is a number prime or not. A positive whole number n > 2 is prime if no number between 2 and sqrt(n) divides n.

Here is my code:

import math

def main():
     print("Prime number or not")
     try:
          N = -1
          while N<2:
              print("Error!Enter numbers greater than two")
              N = int(input("Enter the right number:"))
              values = list(range(2,round(math.sqrt(N))))
              for i in values:
                  if i%N !=0:
                      continue
                  x = print("The number is not prime")
                 elif i%N ==0:
                     break
                 x = print("The number is NOT prime")
           print(x)

    except ValueError:
        print("Error!Print correct number")
    except NameError:
        print("Error!Print the numbers")

main()

But is shows a syntax error in line

elif i%N ==0:

Please, give me some advice how to correct this error and about the code in general. I am new in learning Python, so any help and critic will be good! Thanks.

Your indentation is confused. Can you please re-indent your code, preferably with four spaces? — NightShadeQueen, Jul 20 '15 at 19:00
The `elif` is not connected to the `if` block above it. You can't put other statements between these blocks. — TigerhawkT3, Jul 20 '15 at 19:01
In Python, indentation is part of syntax. Please fix it and update your question accordingly. — Łukasz Rogalski, Jul 20 '15 at 19:06
Seeing `eval(x)` to convert a number makes me sad. Use `int(x)`instead! — Kijewski, Jul 20 '15 at 19:16

score 1 · Accepted Answer · 2021-01-06T23:36:46.820

If you wanted this to be your whole programme, here is my solution:

# Get num
num = input('Input a whole number: ')

# Is num valid
try:
  num = int(num)
  if num < 1 or num > 1000000000000:
    print('Your field cannot be greater than one quantillion or less than one.')
  else:
    # Is num 2 or 5, if yes, prime.
    if num != 2 and num != 5:
      # Is the last number of num 0, 2, 4, 5, 6, or 8, if yes, composite.
      lastNum = str(num)[-1]
      if lastNum == '0' or lastNum == '2' or lastNum == '4' or lastNum == '5' or lastNum == '6' or lastNum == '8':
        print('Your number is composite.')
        if lastNum == '5':
          print(str(num) + ' is divisible by 5.')
        else:
          print(str(num) + ' is divisible by 2.')
      else:
        # List multiples of 3 less than 123, call it multiplesOf3.
        multiplesOf3 = []
        appendMultiple = 0
        for i in range(40):
          appendMultiple += 3
          multiplesOf3.append(appendMultiple)
        # Get sum of all numbers in num, name is sumOfNum
        sumOfNum = 0
        numStr = str(num)
        for i in range(len(numStr)):
          sumOfNum += int(numStr[i])
        # Is sumOfNum in multiplesOf3? 
        numMultipleOf3 = sumOfNum in multiplesOf3
        if numMultipleOf3 == True:
          print('Your number is composite.\n' + str(num) + ' is divisible by 3.')
        else:
          print('Your number is prime.')
    else:
      print('Your number is prime') 
except:
  print('Your field needs to be a whole number. Make sure there is no decimal points (i.e. 12.0 will not be accepted).')

But if you wanted this to be just a function, here is my solution (Make sure you put in a parameter, it requires 1 argument; put in your number.)

 def isPrime(num): 
  try:
    num = int(num)
    if num < 1 or num > 1000000000000:
      print('Your field cannot be greater than one quantillion or less than one.')
    else:
      # Is num 2 or 5, if yes, prime.
      if num != 2 and num != 5:
        # Is the last number of num 0, 2, 4, 5, 6, or 8, if yes, composite.
        lastNum = str(num)[-1]
        if lastNum == '0' or lastNum == '2' or lastNum == '4' or lastNum == '5' or lastNum == '6' or lastNum == '8':
          print('Your number is composite.')
          if lastNum == '5':
            print(str(num) + ' is divisible by 5.')
          else:
            print(str(num) + ' is divisible by 2.')
        else:
          # List multiples of 3 less than 123, call it multiplesOf3.
          multiplesOf3 = []
          appendMultiple = 0
          for i in range(40):
            appendMultiple += 3
            multiplesOf3.append(appendMultiple)
          # Get sum of all numbers in num, name is sumOfNum
          sumOfNum = 0
          numStr = str(num)
          for i in range(len(numStr)):
            sumOfNum += int(numStr[i])
          # Is sumOfNum in multiplesOf3? 
          numMultipleOf3 = sumOfNum in multiplesOf3
          if numMultipleOf3 == True:
            print('Your number is composite.\n' + str(num) + ' is divisible by 3.')
          else:
            print('Your number is prime.')
      else:
        print('Your number is prime') 
  except:
    print('Your field needs to be a whole number. Make sure there is no decimal points (i.e. 12.0 will not be accepted).')

Another way,

def isprime(n):
  if min(n//2,n//3,n//5) == 1:
    return True
  elif min(n%2,n%3,n%5) == 0:
    return False
  return True

This is SO much shorter!

score -1 · Answer 2 · answered Jul 20 '15 at 19:36

assuming that the indentation on the question is correct NOW, the problem is that your elif block doesn't have an if parent. It's also indented wrong, which even if you fix the first error will throw an IndentationError but that's almost beside the point.

for i in values:
    if i%N !=0:
        continue
    x = print("The number is not prime")  # huh? you've left the `if` block
   elif i%N ==0:  # under-indented
       break

Prime number(Python 3)

2 Answers2