REF: simplify coerce_to_target_dtype (pandas-dev#38683)

Author: jbrockmendel

pandas/core/internals/blocks.py

@@ -37,9 +37,7 @@
 from pandas.core.dtypes.common import (
     DT64NS_DTYPE,
     TD64NS_DTYPE,
-    is_bool_dtype,
     is_categorical_dtype,
-    is_datetime64_any_dtype,
     is_datetime64_dtype,
     is_datetime64tz_dtype,
     is_dtype_equal,
@@ -53,7 +51,6 @@
     is_re,
     is_re_compilable,
     is_sparse,
-    is_timedelta64_dtype,
     pandas_dtype,
 )
 from pandas.core.dtypes.dtypes import CategoricalDtype, ExtensionDtype
@@ -927,7 +924,7 @@ def setitem(self, indexer, value):
 
         else:
             # current dtype cannot store value, coerce to common dtype
-
+            # TODO: can we just use coerce_to_target_dtype for all this
             if hasattr(value, "dtype"):
                 dtype = value.dtype
 
@@ -1164,33 +1161,9 @@ def coerce_to_target_dtype(self, other):
         # if we cannot then coerce to object
         dtype, _ = infer_dtype_from(other, pandas_dtype=True)
 
-        if is_dtype_equal(self.dtype, dtype):
-            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)
-
-        elif (self.is_float or self.is_complex) and (
-            is_integer_dtype(dtype) or is_float_dtype(dtype)
-        ):
-            # don't coerce float/complex to int
-            return self
+        new_dtype = find_common_type([self.dtype, dtype])
 
-        elif self.is_datetime or is_datetime64_any_dtype(dtype):
-            # The is_dtype_equal check above ensures that at most one of
-            #  these two conditions hold, so we must cast to object.
-            return self.astype(object)
-
-        elif self.is_timedelta or is_timedelta64_dtype(dtype):
-            # The is_dtype_equal check above ensures that at most one of
-            #  these two conditions hold, so we must cast to object.
-            return self.astype(object)
-
-        try:
-            return self.astype(dtype)
-        except (ValueError, TypeError, OverflowError):
-            return self.astype(object)
+        return self.astype(new_dtype, copy=False)
 
     def interpolate(
         self,