self.__dict__ tricks

[Tim Johnson]

On 2009-10-30, Steven D'Aprano <steve at REMOVE-THIS-cybersource.com.au> wrote:
>
> Could you explain what problem you are trying to solve?
>
>
>> class formLoader():
 
  Hi Steve 
  In a nutshell:
  The 'problem' is to parse a form in such a way that tags which are to
  be modified are represented as dictionaries. The 'grunt' work is
  done.  This class will probably grow with time.

> Idiomatic Python is to use CamelCase for classes.
  Can you point me to a discussion on Idiomatic Python, CamelCase and
  other matters?

> Is your intention to ensure that the only keyword arguments allowed are 
> fileName, record and string?
 Correct.

> Perhaps the easiest way to do that is:
>
> for k in kw:
>     if k not in ('filename', 'record', 'string'):
>         raise Exception()  # whatever...
>     setattr(self, k) = kw[k]
  Understood. A better 'trick'

>> 			else:
>> 				raise AttributeError(
>
> In my opinion, AttributeError is not appropriate here. Passing an invalid 
> parameter shouldn't raise the same error as failing an attribute look-up. 
> That's misleading and confusing.
  What error class or other approach do you recommend?

> [Aside: eight space tabs are *WAY* too big for Usenet and email. You 
> should use four spaces, or even two, when posting here.]
  Yikes! I just starting using vim with slrn again. Will take care of 
  that.

> It is idiomatic Python to use "instance attributes" to refer to 
> attributes attached to instances, and "class attributes" to refer to 
> those attached to classes. Talking about "class members" will confuse 
> Python developers who aren't also familiar with Java or C++. (I know it 
> confuses *me* -- are class members shared by all instances in a class, as 
> the name implies, or are they individual to the instance, as your code 
> implies?)
 Thanks for that. C++ corrupted me.

> I also should point out that your trick will fail if you are using 
> __slots__.
  ??. Will research that. Elaborate if you wish.

>> 		self.tokens = 
> ["form","input","textarea","select","option","form"]
<....>
>
> Is any of that relevant to the trick you are asking for comments for? If 
> not, why is it here?
 It was there to illustrate my edification of the usage of self.__dict__

>> I'd welcome comments - such as any other applications.
>
> Personally, I don't like it. The method signature makes it impossible to 
> tell what arguments are excepted, and it forces me to use keywords even 
> if I'd prefer to use positional arguments. I prefer to let the 
> interpreter check the arguments for me:

  Using your tuple example would clarify things. The method signature
  then becomes the tuple. I.E 

  #<steve sayeth>     
  if k not in ('filename', 'record', 'string'): 
       # handle here 

  If the class grows - and I expect it will - I'd prefer to stick with
  the keywords approach. That approach also allows me to use a
  dictionary to initialize the object.

  Thanks for the input. Very helpful.
  - and always a newbie -
-- 
Tim 
tim at johnsons-web.com
http://www.akwebsoft.com