On Fri, Sep 4, 2020, 12:48 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 >
It will break an ENORMOUS amount of code. Numpy has its own top-level "inf" variable. So all code that uses "from numpy import *" will break. Pylab imports numpy in that way, so "from pylab import *" will also break. Whether you think this is a good approach or not, a ton of tutorials recommend doing this. All of those tutorials will break in a way that is very hard to fix. >
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