On 06/23/2018 11:16 PM, Chris Angelico wrote:
On Sun, Jun 24, 2018 at 4:08 PM, Jim Lee <jle...@gmail.com> wrote:
There are three locals: a, b, and result. Since result cannot be assigned
a value until the list comp has been evaluated, I would expect the comp to
return a value of "None" for result. An argument could also be made for [1,
2, []], but one thing I would *not* expect is [1, 2] or [2, 1]...
Ahh, I see what you mean. Thing is, there's a definite difference
between "this is None" and "this doesn't have a value". The latter
situation is indicated by simply not having the local.
def f():
print("; ".join("%s=%r" % x for x in locals().items()))
a = 1
print("; ".join("%s=%r" % x for x in locals().items()))
b = 2
print("; ".join("%s=%r" % x for x in locals().items()))
The results may surprise you, or may not.
This part has nothing to do with the behaviour of locals inside a
comprehension, though. The important part is that, like me, you would
like comprehensions to represent a block of code inside the current
function, not an implicit nested function.
ChrisA
That's why I said an argument could be made for [1, 2, []]. I realize
that NoneType is not the same as no type, but, having not studied the
internals of any particular Python implementation, I don't know how it
builds or initializes its local symbol table. But, I expected "result"
to exist before the list comprehension was evaluated simply due to
left->right parsing.
-Jim
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