Modifying Class Object

[Alf P. Steinbach]

* MRAB:
> Alf P. Steinbach wrote:
>> * Chris Rebert:
>>> On Sun, Feb 7, 2010 at 5:05 PM, T <misceverything at gmail.com> wrote:
>>>> Ok, just looking for a sanity check here, or maybe something I'm
>>>> missing.  I have a class Test, for example:
>>>>
>>>> class Test:
>>>>    def __init__(self, param1, param2, param3):
>>>>        self.param1 = param1
>>>>        self.param2 = param2
>>>>        self.param3 = param3
>>>>
>>>> Next, I have a dictionary mytest that contains instances of Test.  If
>>>> I want to modify one of the Test instances within my dictionary, I
>>>> have to rewrite the entire entry, correct (since Python passes by
>>>> value, not reference)?
>>>
>>> Incorrect; Python uses neither. See
>>> http://effbot.org/zone/call-by-object.htm for a excellent explanation
>>> of what Python does use.
>>
>> Hm. While most everything I've seen at effbot.org has been clear and 
>> to the point, that particular article reads like a ton of obfuscation.
>>
>> Python passes pointers by value, just as e.g. Java does.
>>
>> There, it needed just 10 words or so. :-) Or perhaps some more words 
>> to point out that in the Java language spec those reference values are 
>> called pointers, but that this terminology isn't (apparently) used for 
>> Python, and isn't even well known among Java programmers. But that's 
>> just one extra little para.
>>
>> One just has to be clear about exactly what it is that's passed by value.
>>
>> Not Python objects, but references (pointers) to them, the id(o) values.
>>
> A reference is not the same as a pointer.

Depends on your choice terminology. I referred to the Java (language spec) 
terminology to make it clear.


> A pointer tells you where something is; a reference doesn't.

Sorry, I don't know of any relevant terminology where that is the case.


Cheers & hth.,

- Alf