PyMyth: Global variables are evil... WRONG!

[Rhodri James]

On Tue, 12 Nov 2013 02:06:09 -0000, Rick Johnson  
<rantingrickjohnson at gmail.com> wrote:

> PyMyth: Global variables are evil... WRONG!

That's not a PyMyth.  It's a CompSciMyth, or to be more accurate a good  
general Software Engineering guideline regardless of language.  Like all  
guidelines it can be broken, but people who break it should do so  
knowingly, aware that they have created potential problems for themselves.

> ============================================================
>  The denial of the 99%:
> ============================================================
> Python has globals, but we just can't admit it!

A different subject entirely, but no more accurately stated.

[snip]
> But even the "module level" globals can be accessed
> "globally" if the module they are contained in is imported
> everywhere.

Remember when I said that guidelines can be broken?

> Globals are justified when they are used to communicate
> information between scopes that otherwise were meant to be
> mutually exclusive. One good example would be package sub-
> modules.

Sometimes, yes.  As long as you don't mind not being thread-safe, etc,  
etc.  If you've designed your interface, you're probably fine.  If you've  
throw it together with globals because it's the easy way, you're about to  
find out why the guideline you're breaking is a good one.

>  "But Rick, even when we use globals, we don't need that many"
>
> Only if you consider the single package that represents your
> program, but what about the thousands of support libraries
> with millions of lines of code that work in the background
> to make your measly few thousand lines of code work?  What
> about all the globals that they have injected?

Didn't you just say that Python globals are really module-level globals?   
Isn't this a strawman you've already disallowed?  It sounds to me like  
you're complaining that Python is ahead of the curve here :-)

-- 
Rhodri James *-* Wildebeest Herder to the Masses