29.09.18 15:19, Steven D'Aprano пише:
On Sat, Sep 29, 2018 at 10:50:24AM +0300, Serhiy Storchaka wrote:
How does it differ from float('nan')?
It is still an integer and would pass through any processing that
expected an integer as one, (with a value of iNaN).
Python is dynamically typed language. What is such processing that would
work with iNaN, but doesn't work with float('nan')?
The most obvious difference is that any code which checks for
isinstance(x, int) will fail with a float NAN.
Yes, an explicit check. But why do you need an explicit check? What will
you do with True returned for iNaN? Can you convert it to a machine
integer or use it as length or index?
If you use MyPy for
static type checking, passing a float NAN to something annotated to only
accept ints will be flagged as an error.
I think that passing iNaN to most of functions which expect int is an
error. Does MyPy supports something like "int | iNaN"? Than it should be
used for functions which accept int and iNaN.
Bitwise operators don't work:
py> NAN = float("nan")
py> NAN & 1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for &: 'float' and 'int'
Now I'm not sure what Steve expects NANs to do with bitwise operators.
But raising TypeError is probably not what we want.
Since these operations make no sense, it makes no sense to discuss them.
A few more operations which aren't supported by floats:
NAN.numerator
NAN.denominator
Do you often use these attributes of ints?
NAN.from_bytes > NAN.bit_length
NAN.to_bytes
What is the meaning of this?
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