CODEWITHSUNDEEP
pythonpython-3.xrange
Help_Steve_Code
Help_Steve_Code

Reputation: 97

Upper bound equal to lower in Python range

Can someone please explain to me why this code works for 2 as well:

def is_prime_v1(n):
  '''Return True if 'n' is prime. False otherwise.'''
  if n == 1:
    return False

  for d in range(2,n):
    if n % d == 0:
      return False

  return True

when the code gets to 

for d in range(2,n):
    if n % d == 0:
      return False
  return True

Would it not see this as start at 2 but go up to and do not include 2? This does not make complete sense to me. The formula works but if you try and create a list on that range like so:

x = list(range(2,2))

You get an empty list.

Please could anyone explain this to me? Does it work for two as well because it would not be able to do the below on range(2,2) and then moves down to return True?

 if n % d == 0:
      return False
  return True

Thanks

Upvotes: 0

Views: 950

Answers (2)

user12364557
user12364557

Reputation:

Your assumption is correct. The upper value of the range function is not put through the for loop. To overcome this, you could just add or n == 2 to the third line of your program.

Upvotes: 1

sahasrara62
sahasrara62

Reputation: 11247

because for loop is never executed , list(range(2,2)) == [], so the program didn't iterate over range and directly proced to return True statement

Upvotes: 1

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