On 17Nov2020 09:55, Mark Shannon <m...@hotpy.org> wrote:
>I'm wondering why
>```
>x = "value"
>try:
> 1/0
>except Exception as x:
> pass
>```
>
>does not restore "value" to x after
>the `except` block.
Because the except is not a new scope. So it is the same "x".
Here:
https://docs.python.org/3/reference/compound_stmts.html#try
it says:
When an exception has been assigned using as target, it is cleared
at the end of the except clause. This is as if
except E as N:
foo
was translated to
except E as N:
try:
foo
finally:
del N
This means the exception must be assigned to a different name to be
able to refer to it after the except clause. Exceptions are cleared
because with the traceback attached to them, they form a reference
cycle with the stack frame, keeping all locals in that frame alive
until the next garbage collection occurs.
>Here's an example of restoring the value of the variable after the
>`except` block:
>
>>>> def f(x):
>... try:
>... 1/0
>... except Exception as x:
>... pass
>... return x
>...
>>>> f("hi")
>'hi'
In the Python 3.8.5 I don't see this:
Python 3.8.5 (default, Jul 21 2020, 10:48:26)
[Clang 11.0.3 (clang-1103.0.32.62)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> def f(x):
... try:
... 1/0
... except Exception as x:
... pass
... return x
...
>>> f(3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 6, in f
UnboundLocalError: local variable 'x' referenced before assignment
and the same outside a function.
Cheers,
Cameron Simpson <c...@cskk.id.au>
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