An "Object" class?

[Cristian Cocos]

Thank you! For some reason I didn't think of using issubclass and
isinstance in my Python types investigation. As you may have already
noticed, I am a Python beginner. I also happen to have a Logic and
Foundations of Mathematics background, hence I am tempted to investigate
Python's type taxonomy from a basic mathematical angle, with an eye to
"recovering" basic mathematical notions such as set membership, set
inclusion etc. So far, I have been living under the impression that type()
is akin to set membership (in a meta-Python approach), hence it should
ideally match the results of isinstance(), but that does not happen:

>>> type(print)
<class 'builtin_function_or_method'>
>>> isinstance(print, builtin_function_or_method)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'builtin_function_or_method' is not defined

Just curious why builtin_function_or_method doesn't work as an argument of
isinstance(). After all,  builtin_function_or_method is a type, right?

The bottom line is that I am trying to figure out where exactly the world
of Python types _diverges from_ what I would expect as a mathematician. It
makes it easier for me to learn Python this way.

Many thanks,

C

On Wed, Aug 28, 2019 at 11:56 PM Alan Bawden <alan at csail.mit.edu> wrote:

> Cristian Cocos <cristi at ieee.org> writes:
>
> > Thank you! I can see that the taxonomy of built-in classes (i.e. the
> > subclass/superclass relations) is not very developed. At the very least I
> > would have loved to see stuff such as int declared as a subClass/subType
> > of float and the like--that is, a class taxonomy in tune with standard
> > mathematical practice, but I am guessing that mathematical kosher-ness
> had
> > to take a back seat to implementational concerns.
>
> Except that numbers of type `int' are _not_ a subset of numbers of
> type `float'!  Some ints are much larger that the largest float.
>
> In fact, both `int' and `float' are subclasses of `numbers.Real'.  While it
> is true that `numbers.Real' does not appear in the list returned by
> `type.mro(int)', nevertheless `issubclass(int, numbers.Real)' and
> `isinstance(2, numbers.Real)' are true.  `type.mro' tells you something
> about the _implementation_ of `int' and `float' that you _usually_
> shouldn't
> concern yourself with.  Stick to `isinstance' and `issubclass' and
> everthing looks pretty kosher.
>
> --
> Alan Bawden
> --
> https://mail.python.org/mailman/listinfo/python-list
>


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