Allow excluding NaT

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: minor
+
+The :func:`~hypothesis.extra.numpy.from_dtype` function no longer generates
+``NaT`` ("not-a-time") values for the ``datetime64`` or ``timedelta64`` dtypes
+if passed ``allow_nan=False`` (:issue:`3943`).

hypothesis-python/src/hypothesis/extra/numpy.py

@@ -219,7 +219,11 @@ def compat_kw(*args, **kw):
             # it here because we'd have to guard against equivalents in arrays()
             # regardless and drawing scalars is a valid use-case.
             res = st.sampled_from(TIME_RESOLUTIONS)
-        result = st.builds(dtype.type, st.integers(-(2**63), 2**63 - 1), res)
+        if allow_nan is not False:
+            elems = st.integers(-(2**63), 2**63 - 1) | st.just("NaT")
+        else:  # NEP-7 defines the NaT value as integer -(2**63)
+            elems = st.integers(-(2**63) + 1, 2**63 - 1)
+        result = st.builds(dtype.type, elems, res)
     else:
         raise InvalidArgument(f"No strategy inference for {dtype}")
     return result.map(dtype.type)

hypothesis-python/tests/numpy/test_from_dtype.py

@@ -181,6 +181,13 @@ def test_arrays_selects_consistent_time_unit(data, dtype_str):
     assert (dtype_str + "[") in arr.dtype.str
 
 
+@pytest.mark.parametrize("dtype", ["m8", "M8"])
+def test_from_dtype_can_include_or_exclude_nat(dtype):
+    find_any(nps.from_dtype(np.dtype(dtype), allow_nan=None), np.isnat)
+    find_any(nps.from_dtype(np.dtype(dtype), allow_nan=True), np.isnat)
+    assert_no_examples(nps.from_dtype(np.dtype(dtype), allow_nan=False), np.isnat)
+
+
 def test_arrays_gives_useful_error_on_inconsistent_time_unit():
     with pytest.raises(InvalidArgument, match="mismatch of time units in dtypes"):
         check_can_generate_examples(