Albert-Jan Roskam wrote:
>
>
> ----- Original Message -----
>
>> From: Peter Otten <__pete...@web.de>
>> To: python-list@python.org
>> Cc:
>> Sent: Sunday, August 3, 2014 11:37 AM
>> Subject: Re: Correct type for a simple "bag of attributes" namespace
>> object
>>
>> Albert-Jan Roskam wrote:
>>
>>> I find the following obscure (to me at least) use of type() useful
>>> exactly for this "bag of attributes" use case:
>>>>>> employee = type("Employee", (object,), {})
>>>>>> employee.name = "John Doe"
>>>>>> employee.position = "Python programmer"
>>>>>> employee.name, employee.position, employee
>>> ('John Doe', 'Python programmer', <class
>> '__main__.Employee'>)
>>
>> Are you sure you know what you are doing? The above is equivalent to
>>
>>>>> class employee:
>> ... name = "John Doe"
>> ... position = "Python programmer"
>> ...
>>>>> employee.name, employee.position, employee
>> ('John Doe', 'Python programmer', <class
>> '__main__.employee'>)
>>>>> type(employee)
>> <class 'type'>
>>
>> Basically you are using classes as instances. While there is no
>> fundamental difference between classes and instances in Python you'll
>> surprise readers of your code and waste some space:
>
> Yes, I know that it is equivalent, but I have always found it kind of ugly
> to use class() just to bundle a number of items.
But that's what you are doing, you just spell it differently.
> Like you are 'announcing
> OOP' (not sure how to put this into words), and then it's merely a simple
> bundle. Or maybe it's just me being silly, because it's even in the Python
> tutorial: https://docs.python.org/2/tutorial/classes.html#odds-and-ends
>
>>>>> import sys
>>>>> sys.getsizeof(employee)
>> 976
>>>>> class Employee: pass
>> ...
>>>>> employee = Employee()
>>>>> employee.name = "John Doe"
>>>>> employee.position = "Python programmer"
>>>>> sys.getsizeof(employee)
>> 64
> Wow, I was not aware of that at all. So they are not equivalent after all.
I think you are misunderstanding what I was trying to say; so to be
explicit:
>>> class Employee: pass
...
>>> sys.getsizeof(Employee)
976
i. e. you have a per-class and per-instance memory consumption. The latter
is smaller, so with regards to memory consumption instantiating only pays
off when there is more than one employee.
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