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


On Fri, Sep 4, 2020 at 9:49 AM Cade Brown <> 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
>>> 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

Cade Brown
Research Assistant @ ICL (Innovative Computing Laboratory)
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