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 <[email protected]> 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: [email protected]
> ICL/College Email: [email protected]
>
>
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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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