On 27/03/2016 16:48, Ned Batchelder wrote:
On Sunday, March 27, 2016 at 10:43:49 AM UTC-4, BartC wrote:
On 27/03/2016 14:47, Dennis Lee Bieber wrote:
Well, that could be done in Python (not so usefully because you can't
take account of such info until a call is attempted), but that's not
what I'm talking about, which is simply allowing:
fn(...)
whether fn has an explicit return or not, and not allowing:
fn # and other kinds of expression
unless some keyword is used. (I've no idea what that might be; all the
best ones are taken. But I've already said a keyword can be emulated via
a dummy function call.)
Python *could* have made it an error to have a useless expression as a
statement. It would prevent certain kinds of errors. But it would also
complicate the language. How do we decide what is a "useless expression"?
Probably one that would raise eyebrows when used as an expression. Such
as 'f()+1', even though f() might have useful side-effects.
As we've seen this might be an expression with a side-effect:
foo.bar
though it would be unusual. Should it be forbidden?
No. The language can require a prefix, or the coder can put it into a
legal form (pass it to a dummy function for example).
And how do we make docstrings, which are simply string literals as
statements? Or do we allow those? Perhaps we only allow those if they
are the first statement in a module, class, or function? How complicated
do we want these criteria to become?
There would be a list of expression terms that can also form independent
statements. Not knowing Python, the list would comprise function calls
(ie. the function call is top node in the AST of the expression), and
docstrings.
(In other languages it might also include assignments and increments.)
The suggestion has also been made only bare names should be disallowed,
which would probably trap most of the errors it causes, early on.
One of Guido's principles in designing Python was to keep it simple,
even where that might mean people could make errors with it. This part
of the language is no different: any expression can be a statement.
Yeah, but even simpler would be that any statement can also be an
expression! He didn't go that far though.
--
Bartc
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