[issue39484] time_ns() and time() cannot be compared on windows

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

To be clear: the following is flawed as an accuracy test, because the *multiplication* by 1e9 introduces additional error.

# int/int: int.__truediv__(int)
>>> abs(t - int(t/10**9 * 1e9))
172

Try this instead, which uses the Fractions module to get the exact error. (The error is converted to a float before printing, for convenience, to show the approximate size of the errors.)

>>> from fractions import Fraction as F
>>> exact = F(t, 10**9)
>>> int_int = t / 10**9
>>> float_float = t / 1e9
>>> int_int_error = F(int_int) - exact
>>> float_float_error = F(float_float) - exact
>>> print(float(int_int_error))
8.85650634765625e-08
>>> print(float(float_float_error))
-1.49853515625e-07

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<https://bugs.python.org/issue39484>
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