On Tue, Jan 13, 2015 at 7:25 AM, John Ladasky
<[email protected]> wrote:
> When I am working inside the class namespace, the print function call on line
> 8 recognizes the name f and prints the dictionary bound to that name.
>
> However, the LIST COMPREHENSION defined inside the class namespace generates
> a NameError.
A list comp is defined with a function call:
>>> def f():
... return [x*x for x in range(4)]
...
>>> dis.dis(f)
2 0 LOAD_CONST 1 (<code object <listcomp> at
0x7fdf25981420, file "<stdin>", line 2>)
3 LOAD_CONST 2 ('f.<locals>.<listcomp>')
6 MAKE_FUNCTION 0
9 LOAD_GLOBAL 0 (range)
12 LOAD_CONST 3 (4)
15 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
18 GET_ITER
19 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
22 RETURN_VALUE
This prevents leakage of the iterator into the enclosing scope.
Personally, I think it's a hack to get around the fact that Python
doesn't have any concept of sub-function-scope (similar to the weird
hack in try/except); if it weren't for that, true nesting would be
easier. As it is, function definitions in class scope have a special
meaning, and that interferes a bit with list comps.
ChrisA
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