Merge remote-tracking branch 'upstream/master' into refactor-rest-of-…

…core

pandas/core/generic.py

@@ -5341,9 +5341,9 @@ def sample(
             )
         elif frac is None and n % 1 != 0:
             raise ValueError("Only integers accepted as `n` values")
-        elif n is None:
-            n = int(round(frac * axis_length))
-        elif frac is not None:
+        elif n is None and frac is not None:
+            n = round(frac * axis_length)
+        elif n is not None and frac is not None:
             raise ValueError("Please enter a value for `frac` OR `n`, not both")
 
         # Check for negative sizes
@@ -6254,7 +6254,7 @@ def convert_dtypes(
                 )
                 for col_name, col in self.items()
             ]
-            return pd.concat(results, axis=1, copy=False)
+            return concat(results, axis=1, copy=False)
 
     # ----------------------------------------------------------------------
     # Filling NA's