MAINT: Use set logic to check dups

pandas/io/parsers.py

@@ -384,7 +384,7 @@ def _validate_integer(name, val, min_val=0):
     return val
 
 
-def _check_dup_names(names):
+def _validate_names(names):
     """
     Check if the `names` parameter contains duplicates.
 
@@ -395,25 +395,20 @@ def _check_dup_names(names):
     ----------
     names : array-like or None
         An array containing a list of the names used for the output DataFrame.
-    """
-
-    if names is None:
-        return
 
-    counts = {}
-    warn_dups = False
-
-    for name in names:
-        if name in counts:
-            warn_dups = True
-            break
+    Returns
+    -------
+    names : array-like or None
+        The original `names` parameter.
+    """
 
-        counts[name] = True
+    if names is not None:
+        if len(names) != len(set(names)):
+            msg = ("Duplicate names specified. This "
+                   "will raise an error in the future.")
+            warnings.warn(msg, FutureWarning, stacklevel=3)
 
-    if warn_dups:
-        msg = ("Duplicate names specified. This "
-               "will raise an error in the future.")
-        warnings.warn(msg, FutureWarning, stacklevel=3)
+    return names
 
 
 def _read(filepath_or_buffer, kwds):
@@ -439,8 +434,7 @@ def _read(filepath_or_buffer, kwds):
     nrows = _validate_integer('nrows', kwds.get('nrows', None))
 
     # Check for duplicates in names.
-    names = kwds.get("names", None)
-    _check_dup_names(names)
+    names = _validate_names(kwds.get("names", None))
 
     # Create the parser.
     parser = TextFileReader(filepath_or_buffer, **kwds)