[Python-Dev] NoneType(None) raises exception

MRAB python at mrabarnett.plus.com
Fri Apr 26 01:56:46 CEST 2013

On 26/04/2013 00:09, Ethan Furman wrote:
> We just fixed NoneType() to return None instead of raising an exception.
> Another use-case for calling NoneType is working with ORMs:
> result = []
> for field in row:
>        type = get_type(field)      # returns int, bool, str, NoneType, ...
>        result.append(type(field))
> if field is None, the resulting call is NoneType(None), and since NoneType doesn't take any parameters we get an exception.
> Is it worth filing a bug to have NoneType accept one optional argument, which defaults to None, and must be None, else
> raise an exception?
> Or should it be:
> class NoneType:
>       def __new__(cls, *args, **kws):
>           return None
> Which is basically what my 2.x none() helper function does...
On the one hand, NoneType(None) seems a strange thing to do.

On the other hand:

     type(value)(value) == value

would return True for the built-in types (will certain exceptions, such
as when value is float("NaN")).

Let's ask the Zen:

Special cases aren't special enough to break the rules.

Although practicality beats purity.

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