eryksun added the comment:
> If exec gets two separate objects as globals and locals,
> the code will be executed as if it were embedded in a
> class definition.
Probably there needs to be more clarification of the compilation context. Class
definitions support lexical closures, whereas source code passed to exec is
compiled at the time of the call, independent of the lexical context.
In the following example, the code objects for both the class body and the
comprehension can access the free variable "a". In CPython, the class body
references the free variable via the LOAD_CLASSDEREF op, and the comprehension
uses the LOAD_DEREF op.
def f():
a = 5
class C:
print(a)
print([a for i in range(5)])
>>> f()
5
[5, 5, 5, 5, 5]
>>> dis.dis(f.__code__.co_consts[2])
3 0 LOAD_NAME 0 (__name__)
3 STORE_NAME 1 (__module__)
6 LOAD_CONST 0 ('f.<locals>.C')
9 STORE_NAME 2 (__qualname__)
4 12 LOAD_NAME 3 (print)
15 LOAD_CLASSDEREF 0 (a)
18 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
21 POP_TOP
5 22 LOAD_NAME 3 (print)
25 LOAD_CLOSURE 0 (a)
28 BUILD_TUPLE 1
31 LOAD_CONST 1 (<code object <listcomp> ...>)
34 LOAD_CONST 2 ('f.<locals>.C.<listcomp>')
37 MAKE_CLOSURE 0
40 LOAD_NAME 4 (range)
43 LOAD_CONST 3 (5)
46 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
49 GET_ITER
50 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
53 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
56 POP_TOP
57 LOAD_CONST 4 (None)
60 RETURN_VALUE
>>> dis.dis(f.__code__.co_consts[2].co_consts[1])
5 0 BUILD_LIST 0
3 LOAD_FAST 0 (.0)
>> 6 FOR_ITER 12 (to 21)
9 STORE_FAST 1 (i)
12 LOAD_DEREF 0 (a)
15 LIST_APPEND 2
18 JUMP_ABSOLUTE 6
>> 21 RETURN_VALUE
----------
nosy: +eryksun
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<http://bugs.python.org/issue24800>
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