Pythonification of the asterisk-based collection packing/unpacking syntax

[Steven D'Aprano]

On Sun, 18 Dec 2011 13:45:35 +1100, Chris Angelico wrote:

> On Sun, Dec 18, 2011 at 11:59 AM, Steven D'Aprano
> <steve+comp.lang.python at pearwood.info> wrote:
>> The usual test of a weakly-typed language is that "1"+1 succeeds (and
>> usually gives 2), as in Perl but not Python. I believe you are
>> confusing weak typing with dynamic typing, a common mistake.
> 
> I'd go stronger than "usually" there. If "1"+1 results in "11", then
> that's not weak typing but rather a convenient syntax for
> stringification - if every object can (or must) provide a to-string
> method, and concatenating anything to a string causes it to be
> stringified, then it's still strongly typed.


For what it's worth, Wikipedia's article on type systems gives Javascript 
as an example of weak typing because it converts "1"+1 to "11". I agree 
with them.

http://en.wikipedia.org/wiki/Type_system

I think that weak and strong typing aren't dichotomies, but extremes in a 
continuum. Assembly languages are entirely weak, since everything is 
bytes and there are no types to check; some academic languages may be 
entire strong; but most real-world languages include elements of both. 
Most commonly coercing ints to floats.

Chris Smith's influence article "What To Know Before Debating Type 
Systems" goes further, suggesting that weak and strong typing are 
meaningless terms. I don't go that far, but you should read his article:

http://cdsmith.wordpress.com/2011/01/09/an-old-article-i-wrote/


> Or is a rich set of automated type-conversion functions evidence of weak
> typing? And if so, then where is the line drawn - is upcasting of int to
> float weak?

To my mind, the distinction that should be drawn is that if two types are 
in some sense the same *kind* of thing, then automatic conversions or 
coercions are weak evidence of weak typing. Since we consider both ints 
and floats to be kinds of numbers, mixed int/float arithmetic is not a 
good example of weak typing. But since numbers and strings are quite 
different kinds of things, mixed str/int operations is a good example of 
weak typing.

But not *entirely* different: numbers can be considered strings of 
digits; and non-digit strings can have numeric values. I don't know of 
any language that allows 1 + "one" to return 2, but such a thing wouldn't 
be impossible.


-- 
Steven