At 07:06 13/04/01 -0700, Emile van Sebille wrote:
>I suspect the answer lies somewhere in the comma converting the parts of the
>list comprehension into a list itself, much as the comma is used in normal
>iteration idiom:
>
>for i in 1,2
As other have pointed out, your're right, that does explain why it works
that way. But...
>>>[[i,j] [1,2,3], for j in 'abc',]
Traceback ( File "<interactive input>", line 1
[[i,j] [1,2,3], for j in 'abc',]
does not work, yet
>>> [[i,j] for i in range(3), for j in range(3)]
[[[0, 1, 2], 0], [[0, 1, 2], 1], [[0, 1, 2], 2]]
work.
I am not advocating that something is wrong; I just want to point out that
some funny things are happening as a side effect of the grammar and/or
compiler. It's impossible to supply a list as part of the list
comprehension syntax, but you can fake it by writing a comma after the for
clause. That's just weird, and unexpected.
Question: this may turn out to be wrong, and it may be fixed in the future;
OTOH, it can be useful, and (in a rather obscure way) consistent with
Python syntax. What's the take on this? Let it be, or fix it, as a
undesirable side effect that don't belong to list comprehensions?
Carlos Ribeiro
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