为什么Python在这里打印出多个值？

Question

I am writing this function to test the primality of numbers, I know that it is not the best code but I would wish it prints out Not prime when a number is not prime and Is prime when a number is prime. The problem is that it prints out Not prime then Is prime for numbers that are not prime... For example this code:

def isPrime(n):
  for i in range(2, n):
    if n%i==0:
        print "Not Prime!"
        break
  print "Is Prime"

isPrime(5)
isPrime(18)
isPrime(11)

Prints out.

Is Prime
Not Prime!
Is Prime
Is Prime

Help me out, What should I do? I am a beginner.

Answer 1

break doesn't exist out of a function -- it just exits a loop. So as soon as you print "Not prime", you exit the loop and move on to the next print statement.

replace the break with the keyword return instead. return will immediately exit the function, returning the value you give the return statement, or None if you just put return with no value next to it.

Answer 2

Here is a fix (python 3)

def isPrime(n):
  prime = True
  for i in range(2, n):
    if n%i==0:
        print("Not Prime!")
        prime = False
        break
  if prime:
      print("Is Prime") 

isPrime(5)
isPrime(18)
isPrime(11)

The problem in the code you posted is that the last print is always executed.