How much of the time is a branch of the None check a single fallback value or attribute access versus how often a suite of statements within the not-None branch?
I definitely check for None very often also. I'm curious what the breakdown is in code I work with.
To the contrary. I read and write code that performs explicit checks
for None all the time. Catching AttributeError is often a code smell
or at least a measure of last resort.
On Sat, Sep 10, 2016 at 6:46 PM, David Mertz <mertz@gnosis.cx> wrote:
> Ok, I have been thinking of the behavior too broadly. I realize now that
> `x?.foo` might still simply raise an AttributeError if x is neither None nor
> a thing with a foo attribute.
>
> The class I wrote is definitely too aggressive for the behavior described.
> On the other hand, by being narrower in behavior there feels like even less
> motivation for new syntax.
>
>
> On Sep 10, 2016 6:29 PM, "MRAB" <python@mrabarnett.plus.com> wrote:
>>
>> On 2016-09-11 02:02, David Mertz wrote:
>>>
>>> On Sat, Sep 10, 2016 at 5:23 PM, Guido van Rossum <guido@python.org
>>> <mailto:guido@python.org>> wrote:
>>>
>>> No. PEP 505 actually solves the problem without ever catching
>>> AttributeError. Please read it.
>>>
>>>
>>> I read it again (I did a year ago, but reviewed it now). I hadn't been
>>> thinking that the *mechanism* of a new None-coalescing operator would
>>> actually be catching an exception. It could (and should) work
>>> differently if it becomes syntax.
>>>
>>> What I was getting at with "essentially" was that it would *do the same
>>> thing* that an AttributeError does. That is, if `x.foo` can't be
>>> evaluated (i.e. x doesn't have an attribute 'foo'), then access is
>>> informally "an error." The hypothetical "x?.foo" catches that "error"
>>> and substitutes a different value. The particular implementation
>>> under-the-hood is less important for most programmers who might use the
>>> construct (and I think documentation would actually give an informal
>>> equivalent as something similar to what I put in the NoneCoalesce class).
>>>
>> x?.foo would lookup attribute 'foo' _unless_ x was None, in which case it
>> would return None. It's simply:
>>
>> None if x is None else x.foo
>>
>> This means that None?.__str__() would return None, not 'None'. (None has
>> an attribute called '__str__', and None.__str__() returns 'None', but it
>> would not be looked up because None is, well, None.)
>>
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