List Comprehensions Enhancement

[Jeremy Hylton]

>>>>> "ms" == skaller  <skaller at maxtal.com.au> writes:

  ms> In case you didn't know -- and hey, I didn't either until
  ms> recently -- Python ALREADY has pattern matching, its just that
  ms> the patterns are simple: the only patterns recognized are

  ms>     variable-name tuple of pattern

  ms> For example:

  ms>     def f((x,y,z)): print x,y,z f((1,2,3))

I've used this feature very occasionally, and it seemed marginally
helpful. However, it can lead to the occasional odd error message:

>>> def times((a,b)):
...     return 42
... 
>>> times((6,9))
42
>>> times("huh?")
Traceback (innermost last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 1, in times
ValueError: unpack sequence of wrong size

Strings are sequences, and sequences are unpacked for the function.  I 
believe the error message is more obscure when it's created by an
extension module using PyArg_ParseTuple.

Jeremy