pandas-dev#34946 Check type of names argument to read_csv, `read_ta…

…ble`, `read_fwf` to not be a `set`.

pandas/io/parsers.py

@@ -397,7 +397,7 @@ def _validate_integer(name, val, min_val=0):
 
 def _validate_names(names):
     """
-    Raise ValueError if the `names` parameter contains duplicates.
+    Raise ValueError if the `names` parameter contains duplicates or has an invalid data type.
 
     Parameters
     ----------
@@ -407,11 +407,13 @@ def _validate_names(names):
     Raises
     ------
     ValueError
-        If names are not unique.
+        If names are not unique or have incosistent ordering (e.g. set).
     """
     if names is not None:
         if len(names) != len(set(names)):
             raise ValueError("Duplicate names are not allowed.")
+        if not is_list_like(names, allow_sets=False):
+            raise ValueError("Names should have consistent ordering. Consider a list instead.")
 
 
 def _read(filepath_or_buffer: FilePathOrBuffer, kwds):