fix(python): Propagate strictness in from_dicts (#15344)

py-polars/polars/_utils/construction/dataframe.py

@@ -555,7 +555,7 @@ def _sequence_of_sequence_to_pydf(
         if unpack_nested:
             dicts = [nt_unpack(d) for d in data]
             pydf = PyDataFrame.from_dicts(
-                dicts, infer_schema_length=infer_schema_length
+                dicts, strict=strict, infer_schema_length=infer_schema_length
             )
         else:
             pydf = PyDataFrame.from_rows(
@@ -675,6 +675,7 @@ def _sequence_of_dict_to_pydf(
         data,
         dicts_schema,
         schema_overrides,
+        strict=strict,
         infer_schema_length=infer_schema_length,
     )
 
@@ -774,7 +775,9 @@ def _sequence_of_dataclasses_to_pydf(
     )
     if unpack_nested:
         dicts = [asdict(md) for md in data]
-        pydf = PyDataFrame.from_dicts(dicts, infer_schema_length=infer_schema_length)
+        pydf = PyDataFrame.from_dicts(
+            dicts, strict=strict, infer_schema_length=infer_schema_length
+        )
     else:
         rows = [astuple(dc) for dc in data]
         pydf = PyDataFrame.from_rows(
@@ -823,7 +826,9 @@ def _sequence_of_pydantic_models_to_pydf(
             if old_pydantic
             else [md.model_dump(mode="python") for md in data]
         )
-        pydf = PyDataFrame.from_dicts(dicts, infer_schema_length=infer_schema_length)
+        pydf = PyDataFrame.from_dicts(
+            dicts, strict=strict, infer_schema_length=infer_schema_length
+        )
 
     elif len(model_fields) > 50:
         # 'from_rows' is the faster codepath for models with a lot of fields...
@@ -836,7 +841,10 @@ def _sequence_of_pydantic_models_to_pydf(
         # ...and 'from_dicts' is faster otherwise
         dicts = [md.__dict__ for md in data]
         pydf = PyDataFrame.from_dicts(
-            dicts, schema=overrides, infer_schema_length=infer_schema_length
+            dicts,
+            schema=overrides,
+            strict=strict,
+            infer_schema_length=infer_schema_length,
         )
 
     if overrides:

py-polars/src/dataframe/construction.rs

@@ -3,6 +3,7 @@ use pyo3::prelude::*;
 
 use super::*;
 use crate::arrow_interop;
+use crate::conversion::any_value::py_object_to_any_value;
 use crate::conversion::{vec_extract_wrapped, Wrap};
 
 #[pymethods]
@@ -20,24 +21,20 @@ impl PyDataFrame {
     }
 
     #[staticmethod]
-    #[pyo3(signature = (data, schema=None, schema_overrides=None, infer_schema_length=None))]
+    #[pyo3(signature = (data, schema=None, schema_overrides=None, strict=true, infer_schema_length=None))]
     pub fn from_dicts(
         py: Python,
         data: &PyAny,
         schema: Option<Wrap<Schema>>,
         schema_overrides: Option<Wrap<Schema>>,
+        strict: bool,
         infer_schema_length: Option<usize>,
     ) -> PyResult<Self> {
         let schema = schema.map(|wrap| wrap.0);
         let schema_overrides = schema_overrides.map(|wrap| wrap.0);
 
-        // If given, read dict fields in schema order.
-        let mut schema_columns = PlIndexSet::new();
-        if let Some(ref s) = schema {
-            schema_columns.extend(s.iter_names().map(|n| n.to_string()))
-        }
-
-        let (rows, names) = dicts_to_rows(data, infer_schema_length, schema_columns)?;
+        let names = get_schema_names(data, schema.as_ref(), infer_schema_length)?;
+        let rows = dicts_to_rows(data, &names, strict)?;
 
         let schema = schema.or_else(|| {
             Some(columns_names_to_empty_schema(
@@ -138,48 +135,61 @@ where
     Schema::from_iter(fields)
 }
 
-fn dicts_to_rows(
-    records: &PyAny,
-    infer_schema_len: Option<usize>,
-    schema_columns: PlIndexSet<String>,
-) -> PyResult<(Vec<Row>, Vec<String>)> {
-    let infer_schema_len = infer_schema_len
-        .map(|n| std::cmp::max(1, n))
-        .unwrap_or(usize::MAX);
-    let len = records.len()?;
-
-    let key_names = {
-        if !schema_columns.is_empty() {
-            schema_columns
-        } else {
-            let mut inferred_keys = PlIndexSet::new();
-            for d in records.iter()?.take(infer_schema_len) {
-                let d = d?;
-                let d = d.downcast::<PyDict>()?;
-                let keys = d.keys();
-                for name in keys {
-                    let name = name.extract::<String>()?;
-                    inferred_keys.insert(name);
-                }
-            }
-            inferred_keys
-        }
-    };
+fn dicts_to_rows<'a>(data: &'a PyAny, names: &'a [String], strict: bool) -> PyResult<Vec<Row<'a>>> {
+    let len = data.len()?;
     let mut rows = Vec::with_capacity(len);
-
-    for d in records.iter()? {
+    for d in data.iter()? {
         let d = d?;
         let d = d.downcast::<PyDict>()?;
 
-        let mut row = Vec::with_capacity(key_names.len());
-        for k in key_names.iter() {
+        let mut row = Vec::with_capacity(names.len());
+        for k in names.iter() {
             let val = match d.get_item(k)? {
                 None => AnyValue::Null,
-                Some(val) => val.extract::<Wrap<AnyValue>>()?.0,
+                Some(val) => py_object_to_any_value(val, strict)?,
             };
             row.push(val)
         }
         rows.push(Row(row))
     }
-    Ok((rows, key_names.into_iter().collect()))
+    Ok(rows)
+}
+
+/// Either read the given schema, or infer the schema names from the data.
+fn get_schema_names(
+    data: &PyAny,
+    schema: Option<&Schema>,
+    infer_schema_length: Option<usize>,
+) -> PyResult<Vec<String>> {
+    if let Some(schema) = schema {
+        Ok(schema.iter_names().map(|n| n.to_string()).collect())
+    } else {
+        infer_schema_names_from_data(data, infer_schema_length)
+    }
+}
+
+/// Infer schema names from an iterable of dictionaries.
+///
+/// The resulting schema order is determined by the order in which the names are encountered in
+/// the data.
+fn infer_schema_names_from_data(
+    data: &PyAny,
+    infer_schema_length: Option<usize>,
+) -> PyResult<Vec<String>> {
+    let data_len = data.len()?;
+    let infer_schema_length = infer_schema_length
+        .map(|n| std::cmp::max(1, n))
+        .unwrap_or(data_len);
+
+    let mut names = PlIndexSet::new();
+    for d in data.iter()?.take(infer_schema_length) {
+        let d = d?;
+        let d = d.downcast::<PyDict>()?;
+        let keys = d.keys();
+        for name in keys {
+            let name = name.extract::<String>()?;
+            names.insert(name);
+        }
+    }
+    Ok(names.into_iter().collect())
 }

py-polars/tests/unit/constructors/test_dataframe.py

@@ -126,3 +126,16 @@ def test_df_init_from_series_strict() -> None:
 def test_df_init_rows_overrides_non_existing() -> None:
     with pytest.raises(pl.SchemaError, match="nonexistent column"):
         pl.DataFrame([{"a": 1, "b": 2}], schema_overrides={"c": pl.Int8})
+
+
+# https://github.com/pola-rs/polars/issues/15245
+def test_df_init_nested_mixed_types() -> None:
+    data = [{"key": [{"value": 1}, {"value": 1.0}]}]
+
+    with pytest.raises(TypeError, match="unexpected value"):
+        pl.DataFrame(data, strict=True)
+
+    df = pl.DataFrame(data, strict=False)
+
+    assert df.schema == {"key": pl.List(pl.Struct({"value": pl.Float64}))}
+    assert df.to_dicts() == [{"key": [{"value": 1.0}, {"value": 1.0}]}]

py-polars/tests/unit/interop/test_interop.py

@@ -308,7 +308,9 @@ def test_from_dicts() -> None:
 def test_from_dict_no_inference() -> None:
     schema = {"a": pl.String}
     data = [{"a": "aa"}]
-    pl.from_dicts(data, schema_overrides=schema, infer_schema_length=0)
+    df = pl.from_dicts(data, schema_overrides=schema, infer_schema_length=0)
+    assert df.schema == schema
+    assert df.to_dicts() == data
 
 
 def test_from_dicts_schema_override() -> None: