From 422975dee43530588b78d160446c70fda7335ff3 Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Thu, 11 Nov 2021 20:06:42 +0100
Subject: [PATCH] add PyType::is_subclass_of and PyAny::is_instance_of

which get the type to check against as an arguments,
as opposed to a compile-time generic type.
---
 src/types/any.rs          | 19 ++++++++++++++-
 src/types/typeobject.rs   | 50 ++++++++++++++++++++++++++++++++++++---
 tests/test_inheritance.rs | 18 ++++++++++++++
 3 files changed, 83 insertions(+), 4 deletions(-)

diff --git a/src/types/any.rs b/src/types/any.rs
index 8fc8640d4e3..08ddc010246 100644
--- a/src/types/any.rs
+++ b/src/types/any.rs
@@ -667,11 +667,19 @@ impl PyAny {
 
     /// Checks whether this object is an instance of type `T`.
     ///
-    /// This is equivalent to the Python expression `isinstance(self, T)`.
+    /// This is equivalent to the Python expression `isinstance(self, T)`,
+    /// if the type `T` is known at compile time.
     pub fn is_instance<T: PyTypeObject>(&self) -> PyResult<bool> {
         T::type_object(self.py()).is_instance(self)
     }
 
+    /// Checks whether this object is an instance of type `T`.
+    ///
+    /// This is equivalent to the Python expression `isinstance(self, typ)`.
+    pub fn is_instance_of(&self, typ: &PyType) -> PyResult<bool> {
+        typ.is_instance(self)
+    }
+
     /// Returns a GIL marker constrained to the lifetime of this type.
     #[inline]
     pub fn py(&self) -> Python<'_> {
@@ -682,6 +690,7 @@ impl PyAny {
 #[cfg(test)]
 mod tests {
     use crate::{
+        type_object::PyTypeObject,
         types::{IntoPyDict, PyList, PyLong, PyModule},
         Python, ToPyObject,
     };
@@ -782,4 +791,12 @@ mod tests {
             assert!(l.is_instance::<PyList>().unwrap());
         });
     }
+
+    #[test]
+    fn test_any_isinstance_of() {
+        Python::with_gil(|py| {
+            let l = vec![1u8, 2].to_object(py).into_ref(py);
+            assert!(l.is_instance_of(PyList::type_object(py)).unwrap());
+        });
+    }
 }
diff --git a/src/types/typeobject.rs b/src/types/typeobject.rs
index 09a1f8f29ec..ef1bf589eb2 100644
--- a/src/types/typeobject.rs
+++ b/src/types/typeobject.rs
@@ -40,9 +40,10 @@ impl PyType {
         self.getattr("__qualname__")?.extract()
     }
 
-    /// Checks whether `self` is subclass of type `T`.
+    /// Checks whether `self` is a subclass of type `T`.
     ///
-    /// Equivalent to Python's `issubclass` function.
+    /// Equivalent to the Python expression `issubclass(self, T)`, if the type
+    /// `T` is known at compile time.
     pub fn is_subclass<T>(&self) -> PyResult<bool>
     where
         T: PyTypeObject,
@@ -53,12 +54,55 @@ impl PyType {
         Ok(result == 1)
     }
 
+    /// Checks whether `self` is a subclass of `other`.
+    ///
+    /// Equivalent to the Python expression `issubclass(self, other)`.
+    pub fn is_subclass_of(&self, other: &PyType) -> PyResult<bool> {
+        let result = unsafe { ffi::PyObject_IsSubclass(self.as_ptr(), other.as_ptr()) };
+        err::error_on_minusone(self.py(), result)?;
+        Ok(result == 1)
+    }
+
     /// Check whether `obj` is an instance of `self`.
     ///
-    /// Equivalent to Python's `isinstance` function.
+    /// Equivalent to the Python expression `isinstance(obj, self)`.
     pub fn is_instance<T: AsPyPointer>(&self, obj: &T) -> PyResult<bool> {
         let result = unsafe { ffi::PyObject_IsInstance(obj.as_ptr(), self.as_ptr()) };
         err::error_on_minusone(self.py(), result)?;
         Ok(result == 1)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        type_object::PyTypeObject,
+        types::{PyBool, PyLong},
+        Python, ToPyObject,
+    };
+
+    #[test]
+    fn test_type_is_subclass() {
+        Python::with_gil(|py| {
+            assert!(PyBool::type_object(py).is_subclass::<PyLong>().unwrap());
+        });
+    }
+
+    #[test]
+    fn test_type_is_subclass_of() {
+        Python::with_gil(|py| {
+            let bool_type = PyBool::type_object(py);
+            let long_type = PyLong::type_object(py);
+            assert!(bool_type.is_subclass_of(long_type).unwrap());
+        });
+    }
+
+    #[test]
+    fn test_type_is_instance() {
+        Python::with_gil(|py| {
+            let bool_type = PyBool::type_object(py);
+            let obj = false.to_object(py);
+            assert!(bool_type.is_instance(&obj).unwrap());
+        });
+    }
+}
diff --git a/tests/test_inheritance.rs b/tests/test_inheritance.rs
index 01b124b8be9..8dcdd9b6ac6 100644
--- a/tests/test_inheritance.rs
+++ b/tests/test_inheritance.rs
@@ -1,5 +1,6 @@
 use pyo3::prelude::*;
 use pyo3::py_run;
+use pyo3::type_object::PyTypeObject;
 
 use pyo3::types::IntoPyDict;
 
@@ -102,6 +103,23 @@ fn mutation_fails() {
     assert_eq!(&e.to_string(), "RuntimeError: Already borrowed")
 }
 
+#[test]
+fn is_subclass_and_is_instance() {
+    let gil = Python::acquire_gil();
+    let py = gil.python();
+
+    let sub_ty = SubClass::type_object(py);
+    let base_ty = BaseClass::type_object(py);
+    assert!(sub_ty.is_subclass::<BaseClass>().unwrap());
+    assert!(sub_ty.is_subclass_of(base_ty).unwrap());
+
+    let obj = PyCell::new(py, SubClass::new()).unwrap();
+    assert!(obj.is_instance::<SubClass>().unwrap());
+    assert!(obj.is_instance::<BaseClass>().unwrap());
+    assert!(obj.is_instance_of(sub_ty).unwrap());
+    assert!(obj.is_instance_of(base_ty).unwrap());
+}
+
 #[pyclass(subclass)]
 struct BaseClassWithResult {
     _val: usize,