[Python-Dev] PEP 343 - next steps

[Nick Coghlan]

Andrew Koenig wrote:
> Of course, this usage shows that the syntax is unnecessary in this context,
> but what I care about is
> 
> 	def f(x as (a, b)):
> 		# ...
> 
> which has the advantage over the alternative
> 
> 	def f(x):
> 		(a, b) = x
> 		# ...
> 
> that if you call f with the wrong arguments, you get a clearer diagnostic
> message.

Doesn't tuple unpacking give you what you want here already?

Py> def f((a, b)):
...   print a, b
...
Py> f(1, 2)
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: f() takes exactly 1 argument (2 given)
Py> f((1, 2))
1 2

A couple of more complex examples:

Py> def f((a, b), (c, d)):
...   print a, b, c, d
...
Py> f((1, 2), (3, 4))
1 2 3 4

Py> def f((a, b, (c, d))):
...   print a, b, c, d
...
Py> f((1, 2, (3, 4)))
1 2 3 4

About the only downside is the need to rebuild the tuple if you 
actually need it.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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