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Re: Correct type for a simple "bag of attributes" namespace object

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From Peter Otten <__peter__@web.de>
Subject Re: Correct type for a simple "bag of attributes" namespace object
Date Sun, 03 Aug 2014 13:23:42 +0200
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Albert-Jan Roskam wrote:

> 
> 
> ----- Original Message -----
> 
>> From: Peter Otten <__peter__@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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3 Suggestions to Make Python Easier For Children Mark Summerfield <list@qtrac.plus.com> - 2014-08-01 23:45 -0700
  Re: 3 Suggestions to Make Python Easier For Children Marko Rauhamaa <marko@pacujo.net> - 2014-08-02 10:14 +0300
    Re: 3 Suggestions to Make Python Easier For Children Mark Summerfield <list@qtrac.plus.com> - 2014-08-02 00:38 -0700
      Re: 3 Suggestions to Make Python Easier For Children Marko Rauhamaa <marko@pacujo.net> - 2014-08-02 11:03 +0300
        Re: 3 Suggestions to Make Python Easier For Children Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-03 02:00 +1000
          Re: 3 Suggestions to Make Python Easier For Children Marko Rauhamaa <marko@pacujo.net> - 2014-08-02 20:07 +0300
            Re: 3 Suggestions to Make Python Easier For Children Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-02 18:29 +0100
              Re: 3 Suggestions to Make Python Easier For Children Marko Rauhamaa <marko@pacujo.net> - 2014-08-02 21:33 +0300
    Re: 3 Suggestions to Make Python Easier For Children Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-03 01:43 +1000
      Correct type for a simple “bag of attributes” namespace object (was: 3 Suggestions to Make Python Easier For Children) Ben Finney <ben+python@benfinney.id.au> - 2014-08-03 05:58 +1000
        Re: Correct type for a simple "bag of attributes" namespace object (was: 3 Suggestions to Make Python Easier For Children) Mark Summerfield <list@qtrac.plus.com> - 2014-08-02 13:46 -0700
          Re: Correct type for a simple "bag of attributes" namespace object (was: 3 Suggestions to Make Python Easier For Children) Chris Angelico <rosuav@gmail.com> - 2014-08-03 07:05 +1000
          Re: Correct type for a simple "bag of attributes" namespace object Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-02 22:16 +0100
          Re: Correct type for a simple "bag of attributes" namespace object Chris Angelico <rosuav@gmail.com> - 2014-08-03 07:24 +1000
          Re: Correct type for a simple "bag of attributes" namespace object Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-02 22:23 +0100
          Re: Correct type for a simple "bag of attributes" namespace object (was: 3 Suggestions to Make Python Easier For Children) Devin Jeanpierre <jeanpierreda@gmail.com> - 2014-08-02 16:18 -0700
          Re: Correct type for a simple "bag of attributes" namespace object (was: 3 Suggestions to Make Python Easier For Children) Chris Angelico <rosuav@gmail.com> - 2014-08-03 09:27 +1000
          Re: Correct type for a simple "bag of attributes" namespace object (was: 3 Suggestions to Make Python Easier For Children) Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-02 18:59 -0600
          Re: Correct type for a simple "bag of attributes" namespace object Terry Reedy <tjreedy@udel.edu> - 2014-08-02 22:40 -0400
          Re: Correct type for a simple "bag of attributes" namespace object Terry Reedy <tjreedy@udel.edu> - 2014-08-02 22:43 -0400
          Re: Correct type for a simple "bag of attributes" namespace object Albert-Jan Roskam <fomcl@yahoo.com> - 2014-08-03 02:17 -0700
          Re: Correct type for a simple "bag of attributes" namespace object Peter Otten <__peter__@web.de> - 2014-08-03 11:37 +0200
          Re: Correct type for a simple "bag of attributes" namespace object Albert-Jan Roskam <fomcl@yahoo.com> - 2014-08-03 03:51 -0700
          Re: Correct type for a simple "bag of attributes" namespace object Albert-Jan Roskam <fomcl@yahoo.com> - 2014-08-03 04:14 -0700
          Re: Correct type for a simple "bag of attributes" namespace object Peter Otten <__peter__@web.de> - 2014-08-03 13:23 +0200
            Re: Correct type for a simple "bag of attributes" namespace object Marko Rauhamaa <marko@pacujo.net> - 2014-08-03 17:51 +0300
              Re: Correct type for a simple "bag of attributes" namespace object Roy Smith <roy@panix.com> - 2014-08-03 11:09 -0400
                Re: Correct type for a simple "bag of attributes" namespace object Marko Rauhamaa <marko@pacujo.net> - 2014-08-03 18:52 +0300
              Re: Correct type for a simple "bag of attributes" namespace object Terry Reedy <tjreedy@udel.edu> - 2014-08-03 18:55 -0400
                Re: Correct type for a simple "bag of attributes" namespace object Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-04 11:19 +1000
                Re: Correct type for a simple "bag of attributes" namespace object Terry Reedy <tjreedy@udel.edu> - 2014-08-04 01:26 -0400
              Re: Correct type for a simple "bag of attributes" namespace object Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-04 10:13 +1000
                Re: Correct type for a simple "bag of attributes" namespace object Roy Smith <roy@panix.com> - 2014-08-03 20:59 -0400
                Re: Correct type for a simple "bag of attributes" namespace object Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-08-04 13:00 +1200
                Re: Correct type for a simple "bag of attributes" namespace object Marko Rauhamaa <marko@pacujo.net> - 2014-08-04 08:41 +0300
                Re: Correct type for a simple "bag of attributes" namespace object Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-04 00:41 -0600
                Re: Correct type for a simple "bag of attributes" namespace object Marko Rauhamaa <marko@pacujo.net> - 2014-08-04 09:57 +0300
          Re: Correct type for a simple "bag of attributes" namespace object Akira Li <4kir4.1i@gmail.com> - 2014-08-03 18:22 +0400
      Re: Correct type for a simple “bag of attributes” namespace object Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-03 13:28 +0100
        Re: Correct type for a simple “bag of attributes” namespace object Roy Smith <roy@panix.com> - 2014-08-03 08:40 -0400
          Re: Correct type for a simple “bag of attributes” namespace object Chris Angelico <rosuav@gmail.com> - 2014-08-03 22:56 +1000
            Re: Correct type for a simple “bag of attributes” namespace object Roy Smith <roy@panix.com> - 2014-08-03 09:25 -0400
              Re: Correct type for a simple “bag of attributes” namespace object Chris Angelico <rosuav@gmail.com> - 2014-08-03 23:35 +1000
                Re: Correct type for a simple “bag of attributes” namespace object Roy Smith <roy@panix.com> - 2014-08-03 10:36 -0400
                Re: Correct type for a simple “bag of attributes” namespace object Chris Angelico <rosuav@gmail.com> - 2014-08-04 01:00 +1000
      Re: Correct type for a simple “bag of attributes” namespace object Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-03 18:38 +0100
        Re: Correct type for a simple “bag of attributes” namespace object Roy Smith <roy@panix.com> - 2014-08-03 13:44 -0400
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    Re: 3 Suggestions to Make Python Easier For Children Mark Summerfield <list@qtrac.plus.com> - 2014-08-02 01:03 -0700
      Re: 3 Suggestions to Make Python Easier For Children Terry Reedy <tjreedy@udel.edu> - 2014-08-02 19:14 -0400
  Re: 3 Suggestions to Make Python Easier For Children Terry Reedy <tjreedy@udel.edu> - 2014-08-02 19:12 -0400
  Re: 3 Suggestions to Make Python Easier For Children Brian Blais <bblais@gmail.com> - 2014-08-05 07:36 -0400
    Re: 3 Suggestions to Make Python Easier For Children Marko Rauhamaa <marko@pacujo.net> - 2014-08-05 15:04 +0300
      Re: 3 Suggestions to Make Python Easier For Children Skip Montanaro <skip@pobox.com> - 2014-08-05 07:31 -0500
        Re: 3 Suggestions to Make Python Easier For Children Marko Rauhamaa <marko@pacujo.net> - 2014-08-05 16:19 +0300
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        Re: 3 Suggestions to Make Python Easier For Children Chris Angelico <rosuav@gmail.com> - 2014-08-05 23:08 +1000
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