[Tutor] Created Function, Need Argument to be a String

Bryon Adams bryonadams at openmailbox.org
Mon Dec 12 11:29:20 EST 2016

Is there a way to force my argument to always be a string before 
entering the function? Else, is there a better way to go about this? In 
whatever program I write, I could change what I want as input to be a 
string prior to tossing it into the function but I think it would make 
more sense for my function to already do it. The function otherwise 
works. This is on Python3.5 under Fedora 25

The only other thing I could think of would be to put exceptions in for 
syntax error and whatever else pops up as I go along, though to be 
honest it *should* always be a string that gets dumped into the 
function. Not sure how I'd put the exception together though since it's 
not making it into the function prior to failing.

Error from interpreter: (looks like it's taking issue with it being a 
number it doesn't know how to deal with)

 >>> ip_checker(
   File "<stdin>", line 1
SyntaxError: invalid syntax

My function:

def ip_checker(ip_address):
   Takes one IP address and checks whether it is valid or not.
   # Try to convert to integers
     ip_addr = [int(i) for i in ip_address.split('.')]
   except ValueError:
     print('Invalid characters were entered or an octet is empty, please 
try again.')
     return False

   # Determine how many octets were entered
   if len(ip_addr) != 4:
     print('Incorrect number of octets, please try again.')
     return False

   # Determine validity of first octet
   if ((ip_addr[0] > 223) and (ip_addr[0] < 256)) or (ip_addr[0] == 0):
     print('First octet is reserved or zero.')
     return False

   # Determine if this is a loopback address
   if ip_addr[0] == 127:
     print('I think that was a loopback address, please try again.')
     return False

   # Determine if this is an APIPA address
   if (ip_addr[0] == 169) and (ip_addr[1] == 254):
     print('I think that was an APIPA address, please try again.')
     return False

   # Determine if the last three octets are between 0-255
   for octet in (ip_addr[1], ip_addr[2], ip_addr[3]):
     if octet not in [i for i in range(0,256)]:
       print('Octet too large or too small, please try again.')
       return False
       print('The IP address {} is valid.'.format(ip_address))
       return True

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