A critic of Guido's blog on Python's lambda

Alex Martelli aleax at mac.com
Tue May 9 05:38:14 CEST 2006


Joe Marshall <eval.apply at gmail.com> wrote:
   ...
> If you language allows unnamed integers, unnamed strings, unnamed
> characters, unnamed arrays or aggregates, unnamed floats, unnamed
> expressions, unnamed statements, unnamed argument lists, etc.  why
> *require* a name for trivial functions?

I think it's reasonable to make a name a part of functions, classes and
modules because they may often be involved in tracebacks (in case of
uncaught errors): to me, it makes sense to let an error-diagnosing
tracebacks display packages, modules, classes and functions/methods
involved in the chain of calls leading to the point of error _by name_.

I think it's reasonable to make a name a part of types for a different
reason: new types are rarely meant to be used "just once"; but also, if
during debugging any object is displayed, it's nice to be able to show,
as part of the display, "this object is of type X and ...", with X shown
as a name rather than as a complete (thus lengthy) description. (any
decent interactive shell/debugger will let you drill down into the
details as and when you need to, of course, but a well-chosen name can
be often sufficient during such interactive exploration/debugging
sessions, and therefore save time and effort).

This doesn't stop a programmer from using a meaningless name, of course,
but it does nudge things in the right direction.

> Wouldn't all the other constructs benefit by having a required name as
> well?

I believe this is a delicate style call, but I agree with your
implication that a language should at least _allow_ any object to have a
name (even when such objects are more often constructed on the fly, they
could still usefully borrow the first [or, maybe, the latest] name
they're bound to, if any).  If I was designing a language from scratch,
I'd probably have as the first few fields of any object _at least_...:
    a cell pointing to the type object,
    a utility cell for GC (reference count or generation-count +
markflag)
    a cell pointing to the name object,
    ...rest of the object's value/state to follow...

Indeed, "given an object, how do I get its NAME" (for inspection and
debugging purposes) is the most frequently asked question on
comp.lang.python, and I've grown a bit tired of answering "you can't, an
object in general intrinsically ``has no name'', it might have many or
none at all, blah blah" -- yeah, this is technically true (in today's
Python), but there's no real reason why it should stay that way forever
(IMHO).  If we at least ALLOWED named objects everywhere, this would
further promote the use of names as against mysterious "magic numbers",
since the programmer would KNOW that after
    VAT_MULTIPLIER = 1.19
then displaying in a debugger or other interactive session that
PARTICULAR instance of the value 1.19 would show the name string
'VAT_MULTIPLIER' as well (or no doubt a more structured name constructed
on the fly, identifying package and module-within-package too).

As to what good practices should be more or less mandated by the
language, and what other good practices instead should be just gently
nudged towards, that's an interesting design question in each case; to
me, a cornerstone for answering it is generally _language simplicity_.

When mandating a certain good practice DETRACTS from language
simplicity, make it a matter of convention instead; when so mandating
ENHANCES language simplicity (by not needing the addition of some other
construct, otherwise unneeded in the language), go for the mandate.

Mandating names for _everything_ would complicate the language by
forcing it to provide builtin names for a lot of elementary building
blocks: so for most types of objects it's best to "gently nudge".  For
functions, classes, modules, and packages, I think the naming is
important enough (as explained above) to warrant a syntax including the
name; better, therefore, not to complicate the language by providing
another different syntax in each case just to allow the name to be
omitted -- why encourage a pratice that's best discouraged, at the price
of language simplicity?  This DOES imply that some (functions, modules,
etc) that are fundamental to the language (and needed to build others)
should be provided with a name, but then one tends to do that anyway:
what language *DOESN'T* provide (perhaps in some suitable "trigonometry"
module) elementary functions named (e.g.) sin, cos, tan, ..., to let the
user build richer ones on top of those?


Alex



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