BUG: Period incorrectly allowing np.timedelta64('NaT')

doc/source/whatsnew/v1.4.0.rst

@@ -653,6 +653,7 @@ Period
 ^^^^^^
 - Bug in adding a :class:`Period` object to a ``np.timedelta64`` object incorrectly raising ``TypeError`` (:issue:`44182`)
 - Bug in :meth:`PeriodIndex.to_timestamp` when the index has ``freq="B"`` inferring ``freq="D"`` for its result instead of ``freq="B"`` (:issue:`44105`)
+- Bug in :class:`Period` constructor incorrectly allowing ``np.timedelta64("NaT")`` (:issue:`44507`)
 -
 
 Plotting

pandas/_libs/tslibs/period.pyx

@@ -104,7 +104,7 @@ from pandas._libs.tslibs.nattype cimport (
     _nat_scalar_rules,
     c_NaT as NaT,
     c_nat_strings as nat_strings,
-    is_null_datetimelike,
+    checknull_with_nat,
 )
 from pandas._libs.tslibs.offsets cimport (
     BaseOffset,
@@ -1459,10 +1459,13 @@ def extract_ordinals(ndarray[object] values, freq) -> np.ndarray:
     for i in range(n):
         p = values[i]
 
-        if is_null_datetimelike(p):
+        if checknull_with_nat(p):
             ordinals[i] = NPY_NAT
         elif util.is_integer_object(p):
-            raise TypeError(p)
+            if p == NPY_NAT:
+                ordinals[i] = NPY_NAT
+            else:
+                raise TypeError(p)
         else:
             try:
                 ordinals[i] = p.ordinal
@@ -2473,14 +2476,17 @@ class Period(_Period):
                 converted = other.asfreq(freq)
                 ordinal = converted.ordinal
 
-        elif is_null_datetimelike(value) or (isinstance(value, str) and
-                                             value in nat_strings):
+        elif checknull_with_nat(value) or (isinstance(value, str) and
+                                           value in nat_strings):
             # explicit str check is necessary to avoid raising incorrectly
             #  if we have a non-hashable value.
             ordinal = NPY_NAT
 
         elif isinstance(value, str) or util.is_integer_object(value):
             if util.is_integer_object(value):
+                if value == NPY_NAT:
+                    value = "NaT"
+
                 value = str(value)
             value = value.upper()
             dt, reso = parse_time_string(value, freq)

pandas/tests/arrays/period/test_constructors.py

@@ -96,3 +96,28 @@ def test_from_sequence_disallows_i8():
 
     with pytest.raises(TypeError, match=msg):
         PeriodArray._from_sequence(list(arr.asi8), dtype=arr.dtype)
+
+
+def test_from_td64nat_sequence_raises():
+    # GH#44507
+    td = pd.NaT.to_numpy("m8[ns]")
+
+    dtype = pd.period_range("2005-01-01", periods=3, freq="D").dtype
+
+    arr = np.array([None], dtype=object)
+    arr[0] = td
+
+    msg = "Value must be Period, string, integer, or datetime"
+    with pytest.raises(ValueError, match=msg):
+        PeriodArray._from_sequence(arr, dtype=dtype)
+
+    with pytest.raises(ValueError, match=msg):
+        pd.PeriodIndex(arr, dtype=dtype)
+    with pytest.raises(ValueError, match=msg):
+        pd.Index(arr, dtype=dtype)
+    with pytest.raises(ValueError, match=msg):
+        pd.array(arr, dtype=dtype)
+    with pytest.raises(ValueError, match=msg):
+        pd.Series(arr, dtype=dtype)
+    with pytest.raises(ValueError, match=msg):
+        pd.DataFrame(arr, dtype=dtype)

pandas/tests/scalar/period/test_period.py

@@ -40,6 +40,17 @@
 
 
 class TestPeriodConstruction:
+    def test_from_td64nat_raises(self):
+        # GH#44507
+        td = NaT.to_numpy("m8[ns]")
+
+        msg = "Value must be Period, string, integer, or datetime"
+        with pytest.raises(ValueError, match=msg):
+            Period(td)
+
+        with pytest.raises(ValueError, match=msg):
+            Period(td, freq="D")
+
     def test_construction(self):
         i1 = Period("1/1/2005", freq="M")
         i2 = Period("Jan 2005")