random.triangular returns infinity for finite bounds when their difference overflows

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: "Continuous distribution bounded by given lower and upper limits, and having a given mode value in-between." — Random.triangular docstring.

Expected: A finite sample in [-1e308, 1e308].

Actual: random.triangular(-1e308, 1e308, None) returns -inf after random.seed(0).

import random, math

seed, low, high, mode = inp = (0, -1e308, 1e308, None)
if not (math.isfinite(low) and math.isfinite(high) and low < high and mode is None):
    print("REFUTATION REJECTED:", inp, "invalid input")
else:
    random.seed(seed)
    actual = random.triangular(low, high, mode)
    if not low <= actual <= high:
        print("REFUTATION CONFIRMED:", inp, "actual=", actual, "expected=", (low, high))
    else:
        print("REFUTATION REJECTED:", inp, "sample is within the documented interval")

Output on Python 3.14.6 (Windows-11-10.0.26220-SP0), standard library random:

REFUTATION CONFIRMED: (0, -1e+308, 1e+308, None) actual= -inf expected= (-1e+308, 1e+308)

This report was found and written by an automated property-testing tool I run (bugforge). The reproducer above was executed and its output is pasted unedited; no person reviewed the report before it was filed. The search script is in https://github.com/augusto-rehfeldt/bugforge-results/tree/main/random-20261003-034345-c3

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

See #158748 (comment).