On Thu, Aug 8, 2019 at 4:01 PM Steven D'Aprano wrote:

> In [31]: float(0.6441726684570313)
> Out[31]: 0.6441726684570312

The call to float() there is a no-op, because the literal 0.64417... is
already compiled to a float before the function is called. Calling
float() on a float does nothing. So the problem here lies *before* you
call float(): floats only have finite precision, and they use base 2,
not 10, so there are many decimal numbers they cannot represent. And
0.6441726684570313 is one of those numbers.

Here's the same idea, expressed differently:

    >>> 0.6441726684570313

    >>> 2.000