Return and set

Billy Mays 81282ed9a88799d21e77957df2d84bd6514d9af6 at myhashismyemail.com
Tue Jul 19 15:52:52 CEST 2011


On 07/19/2011 09:43 AM, Ben Finney wrote:
> Billy Mays
> <81282ed9a88799d21e77957df2d84bd6514d9af6 at myhashismyemail.com>  writes:
>
>> I have a method getToken() which checks to see if a value is set, and
>> if so, return it. However, it doesn't feel pythonic to me:
>
> Clearly that's because the function name is not Pythonic :-)
>
> I'll assume the name is a PEP-8 compatible ‘get_token’.
>
>> def getToken(self):
>>      if self.tok:
>>          t = self.tok
>>          self.tok = None
>>          return t
>>      # ...
>
> Are you testing ‘self.tok’ in a boolean context because you don't care
> whether it it might be ‘""’ or ‘0’ or ‘0.0’ or ‘[]’ or ‘False’ or lots
> of other things that evaluate false in a boolean context?
>
> If you want to test whether it is any value other than ‘None’, that's
> not the way to do it. Instead, use ‘if self.token is not None’.
>
> But I don't see why you test it at all, in that case, since you're
> immediately setting it to ‘None’ afterward.
>
> Also, the function name is quite misleading; the implication for a
> function named ‘get_foo’ is that it is a non-destructive read. I would
> expect the name of this function to indicate what's going on much more
> explicitly.
>
>
> My suggestion::
>
>      def get_and_reset_token(self):
>          result = self.token
>          self.token = None
>          return result
>

This function is used in a file parser.  There are two methods, 
getToken() and peekToken().  getToken pops a token from the file, while 
peekToken keeps the token, but still returns it.

Code:

     def getToken(self):
         if self.tok:
             t = self.tok
             self.tok = None
             return t
         try:
             t = self.gen.next()
         except StopIteration:
             return NULL
         else:
             return t

     def peekToken(self):
         if not self.tok:
             self.tok = self.getToken()
         return self.tok

NULL is an enumerated value I have defined above.  The idea is for 
peekToken to reuse getToken, but to keep the token still around.







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