On 1/21/2020 11:52 AM, Steven D'Aprano wrote:
I don't really care whether there's documentation for __str__() or
__repr__() or something else. I'm just thinking that there should
be some way to guarantee a well defined "useful" float output
formatting.
https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting
https://docs.python.org/3/library/string.html#format-string-syntax
Thanks. For some reason nobody in #python pointed me to the 'g' format
type. That resolves my issue.
Unfortunately, because 'g' can strip the trailing ".0" floats
formatted with it no longer satisfy the float->str->float
immutability property.
I don't see why. Any string you get back from %g ought to convert back
to a float without loss of precision, the trailing '.0' should not
affect it. Can you give an example where it does?
It seems to work for me.
py> x = 94.0
py> float('%g' % x) == x
True
The reason repr adds the '.0' that 'g' does not is to avoid this problem:
>>> type(eval(repr(17.0))) == type(17.0)
True
>>> type(eval(format(17.0, '.17g'))) == type(17.0)
False
Eric
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