Help vanity plates

I still have a lot to learn but so far I have not been able to solve this problem. If someone can help me a little to solve this problem, I would be very grateful to continue advancing in this course.

def is_valid(s):
  if not s[:2].isalpha(): 
    return False
  if not s[2:].isalnum(): 
    return False
  if len(s) < 2 or len(s) > 6: 
    return False
  if s[2] == '0': 
    return False
  return True

:) plates.py exists
:) input of CS50 yields output of Valid
:) input of ECTO88 yields output of Valid
:) input of NRVOUS yields output of Valid
:) input of CS05 yields output of Invalid
:) input of 50 yields output of Invalid
:( input of CS50P2 yields output of Invalid
    expected "Invalid", not "Valid\n"
:) input of PI3.14 yields output of Invalid
:) input of H yields output of Invalid
:) input of OUTATIME yields output of Invalid