WeichenXu123 commented on a change in pull request #34021:
URL: https://github.com/apache/spark/pull/34021#discussion_r711587577



##########
File path: python/pyspark/sql/dataframe.py
##########
@@ -2536,6 +2536,28 @@ def withColumnRenamed(self, existing, new):
         """
         return DataFrame(self._jdf.withColumnRenamed(existing, new), 
self.sql_ctx)
 
+    def withMetadata(self, columnName, metadata):
+        """Returns a new :class:`DataFrame` by updating an existing column 
with metadata.
+
+        .. versionadded:: 3.3.0
+
+        Parameters
+        ----------
+        columnName : str
+            string, name of the existing column to update the metadata.
+        metadata : dict
+            dict, new metadata to be assigned to df.schema[columnName].metadata
+
+        Examples
+        --------
+        >>> df_meta = df.withMetadata('age', {'foo': 'bar'})
+        >>> df_meta.schema['age'].metadata
+        {'foo': 'bar'}
+        """
+        if not isinstance(metadata, dict):

Review comment:
       @HyukjinKwon 
   
   > 
https://github.com/apache/spark/blob/master/python/pyspark/sql/column.py#L712 
The existing API that takes the metadata also specified that the metadata 
should be a dict in the docstring. However, I'm also fine with not checking the 
dict type.
   
   But in code here 
https://github.com/apache/spark/blob/cabc36b54d7f6633d8b128e511e7049c475b919d/python/pyspark/sql/column.py#L747
 it doesn't require metadata to be dict , so is it a doc error or code error 
there ?




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