Refactor DataFrame filter method to improve type checking for predicates

Author: kosiew

python/datafusion/dataframe.py

@@ -430,9 +430,9 @@ def filter(self, *predicates: Expr) -> DataFrame:
         """
         df = self.df
         for p in predicates:
-            if isinstance(p, str) or not isinstance(p, Expr):
+            if not isinstance(p, Expr):
                 raise TypeError(_EXPR_TYPE_ERROR)
-            df = df.filter(expr_list_to_raw_expr_list(p)[0])
+            df = df.filter(p.expr)
         return DataFrame(df)
 
     def with_column(self, name: str, expr: Expr) -> DataFrame: