API: to_datetime, required unit with numerical (pandas-dev#15836)

* add test_to_datetime_numerical_input
* check arg for numerical type

Author: Anthony Delannoy

pandas/tests/indexes/datetimes/test_tools.py

@@ -688,7 +688,7 @@ def test_to_datetime_types(self):
 
         # ints
         result = Timestamp(0)
-        expected = to_datetime(0)
+        expected = to_datetime(0, unit='ns')
         self.assertEqual(result, expected)
 
         # GH 3888 (strings)
@@ -715,6 +715,13 @@ def test_to_datetime_unprocessable_input(self):
         )
         self.assertRaises(TypeError, to_datetime, [1, '1'], errors='raise')
 
+    def test_to_datetime_numerical_input(self):
+        self.assertRaises(ValueError, to_datetime, arg=int(1000))
+        self.assertRaises(ValueError, to_datetime, arg=float(1000))
+        self.assertRaises(ValueError, to_datetime, arg=range(5))
+        self.assertRaises(ValueError, to_datetime,
+                          arg=np.array(range(5), dtype='d'))
+
     def test_to_datetime_other_datetime64_units(self):
         # 5/25/2012
         scalar = np.int64(1337904000000000).view('M8[us]')

pandas/tseries/tools.py

@@ -437,6 +437,10 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
     if arg is None:
         return None
 
+    check_arg = np.array(arg) if np.iterable(arg) else np.array([arg])
+    if is_numeric_dtype(check_arg) and unit is None:
+        raise ValueError("a unit is required in case of numerical arg")
+
     # handle origin
     if origin == 'julian':