I mentioned that in my post; however it doesn't satisfy the problems I have
(mainly being that eval(repr(x))==x)
I still think unifying it as a constant is better because then the repr of
a float gives a string which, if evaluated, gives the float back exactly.
Using math.inf or string conversion throws an error if you try to evaluate
it
On Fri, Sep 4, 2020, 6:05 PM Christopher Barker <python...@gmail.com> wrote:
> This is in the math module already, along with NaN:
>
> In [1]: import math
>
>
> In [2]: math.inf
>
> Out[2]: inf
>
> In [3]: math.nan
>
> Out[3]: nan
>
> The same value
>
> In [4]: math.inf == float('inf')
>
> Out[4]: True
>
> but not the same object -- i.e. it's not a singleton.
>
> In [5]: math.inf is float('inf')
>
> Out[5]: False
>
> -CHB
>
>
>
> On Fri, Sep 4, 2020 at 9:49 AM Cade Brown <brown.c...@gmail.com> wrote:
>
>> I am positing that Python should contain a constant (similar to True,
>> False, None), called Infinity.
>>
>> It would be equivalent to `float('inf')`, i.e. a floating point value
>> representing a non-fininte value. It would be the positive constant;
>> negative infinity could retrieved via `-Infinity`
>>
>> Or, to keep float representation the same, the name `inf` could be used,
>> but that does not fit Python's normal choice for such identifiers (but
>> indeed, this is what C uses which is the desired behavior of string
>> conversion)
>>
>> I think there are a number of good reasons for this constant. For example:
>> * It is also a fundamental constant (similar to True, False, and None),
>> and should be representable as such in the language
>> * Requiring a cast from float to string is messy, and also obviously
>> less efficient (but this performance difference is likely insignificant)
>> * Further, having a function call for something that should be a
>> constant is a code-smell; in general str -> float conversion may throw an
>> error or anything else and I'd rather not worry about that.
>> * It would make the useful property that `eval(repr(x)) == x` for
>> floating point numbers (currently, `NameError: name 'inf' is not defined
>> `)
>>
>> This makes it difficult to, for example, naively serialize a list of
>> floats. For example:
>>
>> ```
>> >>> x = [1, 2, 3, 4]
>> >>> repr(x)
>> '[1, 2, 3, 4]'
>> >>> eval(repr(x)) == x
>> True
>> >>> x = [1, 2, 3, float('inf')]
>> >>> repr(x)
>> '[1, 2, 3, inf]'
>> >>> eval(repr(x)) == x
>> Traceback (most recent call last):
>> File "<stdin>", line 1, in <module>
>> File "<string>", line 1, in <module>
>> NameError: name 'inf' is not defined
>> ```
>>
>> To me, this is problematic; I would expect it to work seamlessly as it
>> does with other floating point constants.
>>
>> A few rebuttals/claims against:
>> - Creating a new constant (Infinity) which is unassignable may break
>> existing code
>> - Converting a float to string is not the same as it is in C. Whil
>>
>> I also realize that there is `math.inf`, but I argue that the constant is
>> more fundamental than that, and it still doesn't solve the problem with
>> `repr()` I described
>>
>> Thanks,
>> ----
>> *Cade Brown*
>> Research Assistant @ ICL (Innovative Computing Laboratory)
>> Personal Email: brown.c...@gmail.com
>> ICL/College Email: c...@utk.edu
>>
>>
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>
>
> --
> Christopher Barker, PhD
>
> Python Language Consulting
> - Teaching
> - Scientific Software Development
> - Desktop GUI and Web Development
> - wxPython, numpy, scipy, Cython
>
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