Terry J. Reedy added the comment:
This is at most a further doc clarification issue as the code is working as
documented. In a previous issue, I added the following sentence to all current
versions to try to clarify this type of behavior: " If exec gets two separate
objects as globals and locals, the code will be executed as if it were embedded
in a class definition." (This follows " Remember that at module level, globals
and locals are the same dictionary") Let's try it:
class Dummy:
from ctypes import wintypes
print(wintypes.LONG)
class LOGFONT(object):
field = wintypes.LONG
>>>
<class 'ctypes.c_long'>
Traceback (most recent call last):
...
File "F:\Python\mypy\tem.py", line 6, in LOGFONT
field = wintypes.LONG
NameError: name 'wintypes' is not defined
Bingo! Anatoly's result is just as documented.
The doc later says "modifications to the default locals dictionary should not
be attempted." Anatoly's result is an example of why not.
Lets distill the situation:
1. The globals dict and locals mapping passed to exec are either the same
object or different objects. This relation determines the execution behavior.
2. If they are the same object, the code is executed as if at module scope.
They are the same if exec is called with both defaults at module scope, where
globals() is locals(), or if they are explicitly made the same ("globals =
locals()", "locals = globals()", or "globals=dic, locals=dic").
3. If they are different objects, the code is executed as if embedded in a
(dummy) class definition. They are different if exec is called with both
defaults within a class or function scope*, where globals() is not locals(), or
if explicit settings leave them different ("globals = dic" where dic is not
locals(), "locals=map", where map is not globals, or "globals=dic, locals=map",
where dic is not map).
I believe this nails the situation#.
* In 2.x, comprehensions do not create a function scope, but in 3.x, they do.
Lambda expressions always do. This is why I did not write 'within a class or
function definition', as some might not see that as including comprehensions.
# The new last sentence of the second paragraph, quoted above, contradicts the
older first sentence: "In all cases, if the optional parts are omitted, the
code is executed in the current scope." Before 2.2, when the 'current scope' of
a function was limited to global and local namespaces, that sentence was true.
Indeed, it summarized points 1,2,3 above. I believe that it is not true now,
and should be revised, as nonlocal namespaces cannot be seen by exec'ed code. I
believe I checked that before adding the new sentence, but I would recheck
before revising. I am thinking about how to perhaps rewrite the paragraph.
----------
assignee: -> docs@python
components: +Documentation -Interpreter Core
nosy: +docs@python, terry.reedy
stage: -> needs patch
_______________________________________
Python tracker <[email protected]>
<http://bugs.python.org/issue16781>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
