Prevent `str` from converting to `Vec<&str>` and `Vec<String>` (#2500)

CHANGELOG.md

@@ -40,6 +40,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Prevent multiple `#[pymethods]` with the same name for a single `#[pyclass]`. [#2399](https://github.com/PyO3/pyo3/pull/2399)
 - Fixup `lib_name` when using `PYO3_CONFIG_FILE`. [#2404](https://github.com/PyO3/pyo3/pull/2404)
 - Iterators over `PySet` and `PyDict` will now panic if the underlying collection is mutated during the iteration. [#2380](https://github.com/PyO3/pyo3/pull/2380)
+- `FromPyObject::extract` now raises an error if source type is `PyString` and target type is `Vec<T>`. [#2500](https://github.com/PyO3/pyo3/pull/2500)
 
 ### Fixed
 

src/types/sequence.rs

@@ -1,8 +1,8 @@
 // Copyright (c) 2017-present PyO3 Project and Contributors
-
 use crate::err::{self, PyDowncastError, PyErr, PyResult};
+use crate::exceptions::PyValueError;
 use crate::internal_tricks::get_ssize_index;
-use crate::types::{PyAny, PyList, PyTuple};
+use crate::types::{PyAny, PyList, PyString, PyTuple};
 use crate::{ffi, PyNativeType, ToPyObject};
 use crate::{AsPyPointer, IntoPyPointer, Py, Python};
 use crate::{FromPyObject, PyTryFrom};
@@ -270,6 +270,9 @@ where
     T: FromPyObject<'a>,
 {
     fn extract(obj: &'a PyAny) -> PyResult<Self> {
+        if let Ok(true) = obj.is_instance_of::<PyString>() {
+            return Err(PyValueError::new_err("Can't extract `str` to `Vec`"));
+        }
         extract_sequence(obj)
     }
 }
@@ -364,6 +367,19 @@ mod tests {
             assert!(<PySequence as PyTryFrom>::try_from(v.to_object(py).as_ref(py)).is_ok());
         });
     }
+
+    #[test]
+    fn test_strings_cannot_be_extracted_to_vec() {
+        Python::with_gil(|py| {
+            let v = "London Calling";
+            let ob = v.to_object(py);
+
+            assert!(ob.extract::<Vec<&str>>(py).is_err());
+            assert!(ob.extract::<Vec<String>>(py).is_err());
+            assert!(ob.extract::<Vec<char>>(py).is_err());
+        });
+    }
+
     #[test]
     fn test_seq_empty() {
         Python::with_gil(|py| {