Re: [Qemu-devel] [PATCH] iotests: handle TypeError for Python3 in test 242

[Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>]

On 22/02/2019 03:17, Cleber Rosa wrote:
> 
> 
> On 2/18/19 4:25 PM, Philippe Mathieu-Daudé wrote:
>> On 2/18/19 9:05 PM, Eric Blake wrote:
>>> [adding Eduardo for some python 2-vs-3 advice]
>>
>> And Cleber.
>>
>>>
>>> On 2/18/19 1:59 PM, Andrey Shinkevich wrote:
>>>> To write one byte to disk, Python2 may use 'chr' type.
>>>> In Python3, conversion to 'byte' type is required.
>>>>
>>>> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
>>>> ---
>>>>   tests/qemu-iotests/242 | 9 +++++++--
>>>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/tests/qemu-iotests/242 b/tests/qemu-iotests/242
>>>> index 16c65ed..6b1f7b8 100755
>>>> --- a/tests/qemu-iotests/242
>>>> +++ b/tests/qemu-iotests/242
>>>> @@ -65,9 +65,14 @@ def toggle_flag(offset):
>>>>       with open(disk, "r+b") as f:
>>>>           f.seek(offset, 0)
>>>>           c = f.read(1)
>>>> -        toggled = chr(ord(c) ^ bitmap_flag_unknown)
>>>> +        toggled = ord(c) ^ bitmap_flag_unknown
>>>>           f.seek(-1, 1)
>>>> -        f.write(toggled)
>>>> +        try:
>>>> +            # python2
>>>> +            f.write(chr(toggled))
>>>> +        except TypeError:
>>>> +            # python3
>>>> +            f.write(bytes([toggled]))
>>>
>>> Looks like it works, but I'm not enough of a python expert to know if
>>> there is a more Pythonic elegant approach.
>>>
> 
> Well, there's no way around the fact that bytes in Python 3 are very
> different from bytes in Python 2 (just another name for a string).
> 
> What I'd recommend here is to not base the type on the exception, but
> choose it depending on the Python version.  Something like:
> 
> if sys.version_info.major == 2:
>     f.write(chr(toggled))
> else:
>     f.write(bytes([toggled])]
> 
> This is cheaper than raising/catching exceptions, it's self documenting,
> and follows the pattern on other tests.
> 
> Regards,
> - Cleber.
> 

Thank you very much, Cleber.
I would like to write it down as that is in iotests.py :
if sys.version_info.major >= 3:
     ...

>>> If someone else picks it up before my next NBD pull request,
>>> Acked-by: Eric Blake <eblake@redhat.com>
>>>

-- 
With the best regards,
Andrey Shinkevich