Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #62158

Re: Type of an object: ‘obj.__class__’ versus ‘type(obj)’

Show key headers only | View raw

Steven D'Aprano <steve+comp.lang.python@pearwood.info> writes:

> On Mon, 16 Dec 2013 12:51:21 +1100, Ben Finney wrote:
> ... "type(obj)" versus "obj.__class__"
> That is an excellent question, I only wish I had an excellent answer to 
> give you. Obviously great minds think alike because I was going to ask 
> the same question, prompted by this comment from Nick Coghlan on the 
> python-dev list:
>
> "...type(obj).__name__ (working with the concrete type, ignoring any
> proxying) or obj.__class__.__name__ (which takes proxying into 
> account)..."
>
> So there is a difference between them, but I'm not entirely sure what it 
> is.

I understand the difference: sometimes you work with proxies
(e.g. "weakref" proxies). A proxie should work mostly like the proxied
object - but in rare cases, you want to detect that what you have
is actually a proxie rather than the real object.
You can use "type(obj)" to check the real type ob "obj" (in some
sense, it is more direct - more reliable; giving you the real
type of "obj"). "obj.__class__" on the other hand uses standard
attribute access - and proxying may have customized attribute access
to access the proxied object's attributes rather than its own: then
"obj.__class__" would give you not the type of "obj" (the proxie)
but that of the proxied object.

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Type of an object: ‘obj.__class__’ versus ‘type(obj)’ Ben Finney <ben+python@benfinney.id.au> - 2013-12-16 12:51 +1100
  Re: Type of an object: ‘obj.__class__’ versus ‘type(obj)’ Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-12-16 22:17 +0000
    Re: Type of an object: ‘obj.__class__’ versus ‘type(obj)’ dieter <dieter@handshake.de> - 2013-12-17 08:14 +0100
      Re: Type of an object: ‘obj.__class__’ versus ‘type(obj)’ Steven D'Aprano <steve@pearwood.info> - 2013-12-17 07:42 +0000
        Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-17 23:35 +1300
          Re: Type of an object: Ethan Furman <ethan@stoneleaf.us> - 2013-12-17 06:50 -0800
          Re: Type of an object: Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-12-17 15:08 +0000
            Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-18 11:15 +1300
              Re: Type of an object: Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-12-17 23:51 +0000
                Re: Type of an object: Ethan Furman <ethan@stoneleaf.us> - 2013-12-17 17:10 -0800
                Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-19 00:45 +1300
                Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-19 00:39 +1300

csiph-web