check for duplicates in dataframe renaming

polars/polars-core/src/frame/mod.rs

@@ -1,11 +1,11 @@
 //! DataFrame module.
 use std::borrow::Cow;
 use std::collections::HashSet;
-use std::iter::Iterator;
+use std::iter::{FromIterator, Iterator};
 use std::mem;
 use std::sync::Arc;
 
-use ahash::RandomState;
+use ahash::{AHashSet, RandomState};
 use arrow::record_batch::RecordBatch;
 use itertools::Itertools;
 use rayon::prelude::*;
@@ -478,6 +478,14 @@ impl DataFrame {
         if names.len() != self.columns.len() {
             return Err(PolarsError::ShapeMisMatch("the provided slice with column names has not the same size as the DataFrame's width".into()));
         }
+        let unique_names: AHashSet<&str, ahash::RandomState> =
+            AHashSet::from_iter(names.iter().map(|name| name.as_ref()));
+        if unique_names.len() != self.columns.len() {
+            return Err(PolarsError::SchemaMisMatch(
+                "duplicate column names found".into(),
+            ));
+        }
+
         let columns = mem::take(&mut self.columns);
         self.columns = columns
             .into_iter()
@@ -1447,6 +1455,14 @@ impl DataFrame {
         self.select_mut(column)
             .ok_or_else(|| PolarsError::NotFound(name.into()))
             .map(|s| s.rename(name))?;
+
+        let unique_names: AHashSet<&str, ahash::RandomState> =
+            AHashSet::from_iter(self.columns.iter().map(|s| s.name()));
+        if unique_names.len() != self.columns.len() {
+            return Err(PolarsError::SchemaMisMatch(
+                "duplicate column names found".into(),
+            ));
+        }
         Ok(self)
     }
 

py-polars/tests/test_df.py

@@ -1316,3 +1316,12 @@ def test_schema() -> None:
     )
     expected = {"foo": pl.Int64, "bar": pl.Float64, "ham": pl.Utf8}
     assert df.schema == expected
+
+
+def test_df_schema_unique() -> None:
+    df = pl.DataFrame({"a": [1, 2], "b": [3, 4]})
+    with pytest.raises(Exception):
+        df.columns = ["a", "a"]
+
+    with pytest.raises(Exception):
+        df.rename({"b": "a"})