style query: function attributes for return codes?

Steven Bethard steven.bethard at gmail.com
Fri Dec 10 17:43:17 CET 2004


george young wrote:
> [python 2.3.3, x86 linux]
> I recently found myself writing something like:
> 
> def get_connection():
>     if tcp_conn():
>         if server_allows_conn():
>             return 'good_conn'
>         else:
>             return 'bad_auth'
>     else:
>         return 'no_server'
> 
> 
> cn = get_connection()
> if cn == 'good_con': ...
> 
> 
> This is obviously just evil, since a misspelling in the string
> return is treacherous.  I'm considering function attributes:
> 
> def get_connection():
>     if tcp_conn():
>         if server_allows_conn():
>             return get_connection.GOOD
>         else:
>             return get_connection.BAD_AUTH
>     else:
>         return get_connection.NO_SERVER
> get_connection.GOOD = 1
> get_connection.BAD_AUTH = 2
> get_connection.NO_SERVER = 3
> 
> 
> If I put this function in it's own module, the solution is obvious:
> 
> GOOD_CONN = 1
> def get_connection():
>     ...
>         return GOOD_CONN   
> 
> 
> But if this is a small utility function that belongs inside a
> larger module/class, I would like to have it's return values
> closely associated with the function, not just another value in
> the parent class.

Sorry, I also meant to add that the other obvious way of dealing with 
this kind of thing is to make the results keyword parameters:

def get_connection(GOOD=1, BAD_AUTH=2, NO_SERVER=3):
     if tcp_conn():
         if server_allows_conn():
             return GOOD
         else:
             return BAD_AUTH
     else:
         return NO_SERVER

This has the benefit that if your user wants different return values 
they can specify them, but the disadvantage that someone improperly 
calling the function with more than 0 parameters will get, instead of an 
error message, a strange return value.

Steve



More information about the Python-list mailing list