py3: strange behavior of sleep() on Sage types

[embray]

For some reason, passing Python's time.sleep() a Sage RealLiteral less than 1 returns more-or-less immediately:

sage: x = 0.5
sage: type(x)
<class 'sage.rings.real_mpfr.RealLiteral'>
sage: x2 = float(0.5)
sage: type(x2)
<class 'float'>
sage: timeit('sleep(x)')
625 loops, best of 3: 1 µs per loop
sage: timeit('sleep(x2)')
5 loops, best of 3: 500 ms per loop
sage: # One more time for the folks in back...
sage: timeit('sleep(x)')
625 loops, best of 3: 1.01 µs per loop

It's not just in the context of timeit either. 0.5 is long enough that if you do sleep(x2) directly you can feel the delay, whereas with sleep(x) there is much less or even no perceptible delay.''

However,

sage: timeit('sleep(1.0)')
5 loops, best of 3: 1 s per loop

as expected.

The problem appears to stem from the (relatively) new PyTime API, and in particular this function:

static int
_PyTime_FromObject(_PyTime_t *t, PyObject *obj, _PyTime_round_t round,
                   long unit_to_ns)
{
    if (PyFloat_Check(obj)) {
        double d;
        d = PyFloat_AsDouble(obj);
        if (Py_IS_NAN(d)) {
            PyErr_SetString(PyExc_ValueError, "Invalid value NaN (not a number)");
            return -1;
        }
        return _PyTime_FromFloatObject(t, d, round, unit_to_ns);
    }
    else {
        long long sec;
        Py_BUILD_ASSERT(sizeof(long long) <= sizeof(_PyTime_t));

        sec = PyLong_AsLongLong(obj);
        if (sec == -1 && PyErr_Occurred()) {
            if (PyErr_ExceptionMatches(PyExc_OverflowError))
                _PyTime_overflow();
            return -1;
        }

        if (_PyTime_check_mul_overflow(sec, unit_to_ns)) {
            _PyTime_overflow();
            return -1;
        }
        *t = sec * unit_to_ns;
        return 0;
    }
}

So it does not properly handle custom types that implement __float__.

Reported upstream:

• https://bugs.python.org/issue35707
• gh-79888: support __index__ and __float__ in time functions python/cpython#11636

In the meantime I don't see that there's much to be done except to always wrap Sage types in float() before passing them to time functions (or, more extreme, provide our own wrappers for common time functions...)

Upstream: Reported upstream. Developers acknowledge bug.

Component: python3

Issue created by migration from https://trac.sagemath.org/ticket/26311

[vinklein]

comment:2

Thanks for the investigation.

[embray]

comment:4

Retargeting some of my tickets (somewhat optimistically for now).

[jdemeyer]

Upstream: Reported upstream. No feedback yet.

[embray]

comment:6

It feels like there's been a bad habit in CPython lately of needlessly breaking support for custom numerical types.

[jdemeyer]

Changed upstream from Reported upstream. No feedback yet. to Reported upstream. Developers acknowledge bug.

[embray]

comment:8

Yeesh, that thread on bpo is a mess... :(

[jdemeyer]

comment:9

Replying to @embray:

Yeesh, that thread on bpo is a mess... :(

Wait until you see the code. DRY clearly does not apply to the CPython code base: I had to make the same fix 3 times.

[embray]

comment:10

Replying to @jdemeyer:

Replying to @embray:

Yeesh, that thread on bpo is a mess... :(

Wait until you see the code. DRY clearly does not apply to the CPython code base: I had to make the same fix 3 times.

Have you seen Sage's code base? ;)

[embray]

comment:11

Removing most of the rest of my open tickets out of the 8.7 milestone, which should be closed.

[sheerluck]

comment:12

Replying to @jdemeyer:

I had to make the same fix 3 times.

For this ticket 1 time is enough, solved with two line patch:

--- a/Python/pytime.c
+++ b/Python/pytime.c
@@ -404,9 +404,11 @@
 }
 
 static int
-_PyTime_FromObject(_PyTime_t *t, PyObject *obj, _PyTime_round_t round,
+_PyTime_FromObject(_PyTime_t *t, PyObject *xobj, _PyTime_round_t round,
                    long unit_to_ns)
 {
+    PyObject *obj;
+    obj = PyNumber_Float(xobj);
     if (PyFloat_Check(obj)) {
         double d;
         d = PyFloat_AsDouble(obj);

This patch solves only one thing:

TypeError: 'sage.rings.real_mpfr.RealLiteral' object cannot be interpreted as an integer

and only for time.sleep()

I understand that custom builded python is not for everyone.