best way to get data into a new instance?

[James Stroud]

James Stroud wrote:
> John Salerno wrote:
> 
>> Let's pretend I'm creating an Employee class, which I will later 
>> subclass for more specific jobs. Each instance will have stuff like a 
>> name, title, degrees held, etc. etc.
>>
>> So I'm wondering, is the best way to get all this information into the 
>> object to just have a really long __init__ method that takes each 
>> argument?
>>
>> Does a question like this depend on how the class will be used? I'm 
>> trying to construct it in a way that is independent of, say, the GUI 
>> interface that will be used, but I can't help but think that if all 
>> the data is entered into a GUI, then passed programmatically to the 
>> class, then it's no big deal because it happens behind the scenes. But 
>> if, for instance, someone manually created a new instance, they would 
>> have a ton of arguments to type in each time. Granted, even with the 
>> GUI they are basically typing in arguments, but in the manual case 
>> you'd have to type in the call to the class, the parentheses, commas, 
>> quotes around the strings, etc. (But still, I'm trying not to let a 
>> specific interface influence the construction of what should probably 
>> be a completely independent class implementation.)
>>
>> Thanks.
> 
> 
> This assumes that someone will hard-code an instance of your Employee. 
> E.g.:
> 
>      e = Employee(Last, First, ID,
>                   private_medical_info = 'Has halitosis.')
> 
> Will this ever really happen--either by an API user or an end user? 
> Probably not for a database of any usefulness at all. Usually records 
> will be programatically created (or created through a gui), so it really 
> isn't necessary to worry about this case, except maybe for testing. This 
> has been my experience. Its probably better to init with the bare 
> minimum parameters and focus on how to move information from an external 
> source into an already created instance:
> 
>     e = Employee(Last, First, ID)
>     e.private_medical_info = 'Has halitosis.'
> 
> If you are worried about validating field names, maybe use a method:
> 
> class Employee(object):
>   def __init__(self, Last, First, ID, **kwargs):
>     self.Last = Last
>     self.First = First
>     self.ID = ID
>     self._fields = {'Last':'Last Name',
>                     'First':'First Name',
>                     'ID':'Employee Identification Number',
>                     'private_medical_info':'Any source of bad odor.'}
>     for (field, value) in kwargs.items():
>       self.set_value(field, value)
>   def set_value(field, value):
>     if not field in self._fields:
>       raise ValueError, 'Field "%s" not supported.' % field
>     else:
>       self.__setattr__(field, value)
>   def get_value(field):
>     if not field in self._fields:
>       raise ValueError, 'Field "%s" not supported.' % field
>     else:
>       self.__getattribute__(field)
> 
> 
> OK, I'll stop. You get the idea.
> 
> You will find dealing with external sources the more interesting problem 
> anyway.
> 
> James
> 
> 
should be

def set_value(self, field, value):

and

def get_value(self, field):

James

-- 
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/