Re: [PATCH] trace: avoid "is" with a literal Python 3.8 warnings

[Philippe Mathieu-Daudé]

On 10/10/19 2:21 PM, Stefan Hajnoczi wrote:
> The following statement produces a SyntaxWarning with Python 3.8:
>
>    if len(format) is 0:
>    scripts/tracetool/__init__.py:459: SyntaxWarning: "is" with a literal. Did you mean 
> "=="?
>
> Use the conventional len(x) == 0 syntax instead.

Ah this is a new change from 3.8...
https://docs.python.org/3.9/whatsnew/3.8.html

From https://bugs.python.org/issue34850

> Reported-by: Daniel P. Berrangé <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> ---
>   scripts/tracetool/__init__.py | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
> index 04279fa62e..44c118bc2a 100644
> --- a/scripts/tracetool/__init__.py
> +++ b/scripts/tracetool/__init__.py
> @@ -456,12 +456,12 @@ def generate(events, group, format, backends,
>       import tracetool
>   
>       format = str(format)
> -    if len(format) is 0:
> +    if len(format) == 0:
>           raise TracetoolError("format not set")
>       if not tracetool.format.exists(format):
>           raise TracetoolError("unknown format: %s" % format)
>   
> -    if len(backends) is 0:
> +    if len(backends) == 0:
>           raise TracetoolError("no backends specified")
>       for backend in backends:
>           if not tracetool.backend.exists(backend):