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 <pythonchb@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.cade@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.cade@gmail.com ICL/College Email: cade@utk.edu _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/XMA6KOBLPABV7EL5GV2BIRC2ESYKXMVV/ Code of Conduct: http://python.org/psf/codeofconduct/-- Christopher Barker, PhD
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