Objects in Python

[Ben Finney]

lipska the kat <lipskathekat at yahoo.co.uk> writes:

> If, in a language, I find I am able to say
>
> a = 1
>
> then later, in the same scope I can say
>
> a = "foo"
>
> then later again in the same scope I can say
>
> a = ([1,2,3], "xyz", True)
>
> then, and I may be missing something here, to me, that doesn't say
> strongly typed' that says 'no typing constraints whatsoever'

You haven't discovered anything about types; what you have discovered is
that Python name bindings are not variables.

In fact, Python doesn't have variables – not as C or Java programmers
would understand the term. What it has instead are references to objects
(with names as one kind of reference).

The documentation unfortunately calls these references “variables” in
various places, which IMO compounds the confusion in newcomers
experienced with other languages. It's best, I think, to reject the idea
that Python has variables, and think in terms of references instead.

Any reference (with some very narrow specific exclusions, like ‘None’)
can be re-bound to any other object without regard to the previous
binding.

> We need to separate out the 'view' from the 'implementation' here.
> Most developers I know, if looking at the code and without the
> possibly dubious benefit of knowing that in Python 'everything is an
> object' would not call this 'strong typing'

Those people are confused, then. Python is strongly typed: objects
always know their type, the type is always exact, and the type of an
object can't be changed.

This is always true regardless of whether the object is referred to
zero, one, or many times.

Python is dynamically typed: References (and hence names) don't have
types.

> It is OK to to make (possibly erroneous) observations isn't it?

One of our long-time regulars (Aahz, whom I haven't seen for a long
time, sadly) quipped that the best way to get correct information on
Usenet is not to ask a question, but to post incorrect information.
That's not a license for such behaviour, but an observation on its
effectiveness.

I'd say that so long as you phrase your assertions to indicate the level
of confidence and possibility of error, that's okay.

-- 
 \          “Generally speaking, the errors in religion are dangerous; |
  `\    those in philosophy only ridiculous.” —David Hume, _A Treatise |
_o__)                                           of Human Nature_, 1739 |
Ben Finney