[Python-ideas] No implicit variable declarations

[Chris Angelico]

On Sun, Apr 13, 2014 at 2:21 PM, Andrew Barnert
<abarnert at yahoo.com.dmarc.invalid> wrote:
> Of course the cost is that you don't get compile-time type checking. But for many programs, that type checking is nearly useless (at least the Java kind; the Haskell kind is more useful).
>

Aside: I have periodically had bugs where I omit the first argument of
a function (in situations where, had it not been first, it would have
been marked optional). In C, those sorts of bugs are often caught by
the function signature; in Python, they can be, but only if the
function takes a fixed number of args. For instance:

void foo(target *destination, const char *msg, int blah=0, int blahblah=0)

If you omit the destination, you get an error back straight away,
because a string (const char *) can't be converted into a target. The
equivalent in Python, though:

def foo(destination, msg, blah=0, blahblah=0):

would happily assign the args one slot earlier, as long as I provided
at least one of the optionals. But this is a fairly narrow case; if
both those args were mandatory, the mere count of arguments would trip
an error. (Albeit at run-time, not compile-time, but until Python goes
to actually run the line of code, it can't know that this is the
signature anyway.)

ChrisA

PS. Neat trick with dmarc.