Fix dtype coercion

doc/source/whatsnew/v0.22.0.txt

@@ -169,7 +169,7 @@ Conversion
 ^^^^^^^^^^
 
 - Bug in :class:`Index` constructor with `dtype='uint64'` where int-like floats were not coerced to :class:`UInt64Index` (:issue:`18400`)
--
+- Bug in :class:`Block` where math operations on a `DataFrame` containing `bool` as elements are coerced to `bool` in :meth:`coerce_to_target_dtype`.
 -
 
 Indexing

pandas/core/internals.py

@@ -1026,7 +1026,7 @@ def f(m, v, i):
 
         return [self.make_block(new_values, fastpath=True)]
 
-    def coerce_to_target_dtype(self, other):
+    def coerce_to_target_dtype(self, other, force_coericion=False):
         """
         coerce the current block to a dtype compat for other
         we will return a block, possibly object, and not raise
@@ -1042,8 +1042,10 @@ def coerce_to_target_dtype(self, other):
             return self
 
         if self.is_bool or is_object_dtype(dtype) or is_bool_dtype(dtype):
-            # we don't upcast to bool
-            return self.astype(object)
+            if force_coericion and is_float_dtype(dtype) or is_integer_dtype(dtype):
+                return self.astype(dtype)
+            else:
+                return self.astype(object)
 
         elif ((self.is_float or self.is_complex) and
               (is_integer_dtype(dtype) or is_float_dtype(dtype))):
@@ -1324,7 +1326,7 @@ def eval(self, func, other, errors='raise', try_cast=False, mgr=None):
             values, values_mask, other, other_mask = self._try_coerce_args(
                 transf(values), other)
         except TypeError:
-            block = self.coerce_to_target_dtype(orig_other)
+            block = self.coerce_to_target_dtype(orig_other, True)
             return block.eval(func, orig_other,
                               errors=errors,
                               try_cast=try_cast, mgr=mgr)

pandas/tests/frame/test_dtypes.py

@@ -669,6 +669,19 @@ def test_arg_for_errors_in_astype(self):
 
         df.astype(np.int8, errors='ignore')
 
+    from operator import (add, mul, floordiv, sub)
+
+    @pytest.mark.parametrize("num", [1.0, 1])
+    @pytest.mark.parametrize("struct", [pd.Series, pd.DataFrame])
+    @pytest.mark.parametrize('op', [add, mul, floordiv, sub])
+    def test_assert_list_and_bool_coerce(self, num, struct, op):
+        # issue 18549
+        target_type = np.array([op(num, num)]).dtype
+        res = op(struct([True]), num).dtypes
+        if isinstance(res, pd.Series):
+            res = res[0]
+        assert target_type == res
+
 
 class TestDataFrameDatetimeWithTZ(TestData):