Python handles globals badly.
breamoreboy at yahoo.co.uk
Sat Sep 12 05:01:24 CEST 2015
On 12/09/2015 01:01, Michael Torrie wrote:
> On 09/11/2015 03:50 PM, Skybuck Flying wrote:
>> Something which python does not seem to do currently ?!
>> So that's weird.
>> I will leave it at that for now.
> Seems to me you have a completely mistaken understanding of how
> variables work in Python. This is one of the reasons why I have said in
> the past, erroneously, that Python does not have variables. It does of
> course but not in the same way as C or Pascal. In those languages names
> are source-code abstractions only, and irrelevant to the compiler and
> machine code. C and Pascal define variables as boxes that can be
> written to. Not so in Python.
> In Python most common objects are immutable. Meaning they can never
> change or be overwritten. They are bound to names. This binding is
> what makes names look like and act like traditional variables.
> The secret to understanding the global keyword is to understand how
> Python namespaces work. The statement "a=5" does not assign a 5 to the
> box called "a." Rather it binds the name "a" to the "5" object, which
> is immutable and called into existence by the interpreter
> implementation. Subsequently "a=6" disconnects a from the 5 object,
> casting the 5 object loose to be reclaimed in some fashion that doesn't
> matter at this point. "a" is then rebound to a new object, 6.
> When doing a look-up on a name, the interpreter first checks the local
> scope's dictionary and if it does not find the name there there, goes to
> the outer scope and so forth until you get to the module global
> namespace. So we don't need any special keywords to do Pascal-style
> constants. We just define them in the module and they work. Usually we
> name them in all caps so we have a bit of a convention as to where they
> come from. And yes we're talking about looking up strings in a
> dictionary here.
> When binding a name to an object, the interpreter always binds a name in
> the local namespace, unless the global keyword has been used previously
> and then it goes right to the global namespace. As has been said
> numerous times on this thread, how else would the interpreter do this?
> There simply isn't any other way that makes sense. Certainly you haven't
> made the case for it, seeing as you have some fundamental
> misunderstandings about variables in Python.
> You keep saying things like "writing to a variable" or "declared
> variables" which just don't apply to Python because that's not how
> Python variables work. It may appear this way on the surface, but the
> differences are subtle yet important. Namespaces are written to, not
> variables, some objects can be mutated. Names are bound to objects, but
> variables are not declared, as a name can be bound to an object of any type.
> Namespaces are powerful constructs that give Python much of its dynamic
> nature and expressivity. Learn to use them!
My favourite analogy for Python names, the sticky note, here
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.
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