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

[George Fischhof]

2016-12-12 17:29 GMT+01:00 Bryon Adams <bryonadams at openmailbox.org>:

> 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(169.254.0.1)
>   File "<stdin>", line 1
>     ip_checker(169.254.0.1)
>                        ^
> 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
>   try:
>     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
>     else:
>       print('The IP address {} is valid.'.format(ip_address))
>       return True
>
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Hi Btryon,

to to force to process a string is convert the function argument to string:


def ip_checker(ip_address):
  '''
  Takes one IP address and checks whether it is valid or not.
  '''
  ip_address = str(ip_address)

And after this you can process it as a string.


To write more readable and more beautiful code, You can put all your
checkings into small functions inside the ip_checker function:




def ip_checker(ip_address):
    def determine_validity_of_first_octet():
    ....

    def determine_if_this_is_a_loopback():

    ...

    determine_validity_of_first_octet()
    determine ...

and so on
:-)

BR.
George