pyo3/
pycell.rs

1//! PyO3's interior mutability primitive.
2//!
3//! Rust has strict aliasing rules - you can either have any number of immutable (shared) references or one mutable
4//! reference. Python's ownership model is the complete opposite of that - any Python object
5//! can be referenced any number of times, and mutation is allowed from any reference.
6//!
7//! PyO3 deals with these differences by employing the [Interior Mutability]
8//! pattern. This requires that PyO3 enforces the borrowing rules and it has two mechanisms for
9//! doing so:
10//! - Statically it can enforce thread-safe access with the [`Python<'py>`](crate::Python) token.
11//!   All Rust code holding that token, or anything derived from it, can assume that they have
12//!   safe access to the Python interpreter's state. For this reason all the native Python objects
13//!   can be mutated through shared references.
14//! - However, methods and functions in Rust usually *do* need `&mut` references. While PyO3 can
15//!   use the [`Python<'py>`](crate::Python) token to guarantee thread-safe access to them, it cannot
16//!   statically guarantee uniqueness of `&mut` references. As such those references have to be tracked
17//!   dynamically at runtime, using `PyCell` and the other types defined in this module. This works
18//!   similar to std's [`RefCell`](std::cell::RefCell) type.
19//!
20//! # When *not* to use PyCell
21//!
22//! Usually you can use `&mut` references as method and function receivers and arguments, and you
23//! won't need to use `PyCell` directly:
24//!
25//! ```rust,no_run
26//! use pyo3::prelude::*;
27//!
28//! #[pyclass]
29//! struct Number {
30//!     inner: u32,
31//! }
32//!
33//! #[pymethods]
34//! impl Number {
35//!     fn increment(&mut self) {
36//!         self.inner += 1;
37//!     }
38//! }
39//! ```
40//!
41//! The [`#[pymethods]`](crate::pymethods) proc macro will generate this wrapper function (and more),
42//! using `PyCell` under the hood:
43//!
44//! ```rust,ignore
45//! # use pyo3::prelude::*;
46//! # #[pyclass]
47//! # struct Number {
48//! #    inner: u32,
49//! # }
50//! #
51//! # #[pymethods]
52//! # impl Number {
53//! #    fn increment(&mut self) {
54//! #        self.inner += 1;
55//! #    }
56//! # }
57//! #
58//! // The function which is exported to Python looks roughly like the following
59//! unsafe extern "C" fn __pymethod_increment__(
60//!     _slf: *mut pyo3::ffi::PyObject,
61//!     _args: *mut pyo3::ffi::PyObject,
62//! ) -> *mut pyo3::ffi::PyObject {
63//!     use :: pyo3 as _pyo3;
64//!     _pyo3::impl_::trampoline::noargs(_slf, _args, |py, _slf| {
65//! #       #[allow(deprecated)]
66//!         let _cell = py
67//!             .from_borrowed_ptr::<_pyo3::PyAny>(_slf)
68//!             .downcast::<_pyo3::PyCell<Number>>()?;
69//!         let mut _ref = _cell.try_borrow_mut()?;
70//!         let _slf: &mut Number = &mut *_ref;
71//!         _pyo3::impl_::callback::convert(py, Number::increment(_slf))
72//!     })
73//! }
74//! ```
75//!
76//! # When to use PyCell
77//! ## Using pyclasses from Rust
78//!
79//! However, we *do* need `PyCell` if we want to call its methods from Rust:
80//! ```rust
81//! # use pyo3::prelude::*;
82//! #
83//! # #[pyclass]
84//! # struct Number {
85//! #     inner: u32,
86//! # }
87//! #
88//! # #[pymethods]
89//! # impl Number {
90//! #     fn increment(&mut self) {
91//! #         self.inner += 1;
92//! #     }
93//! # }
94//! # fn main() -> PyResult<()> {
95//! Python::with_gil(|py| {
96//!     let n = Py::new(py, Number { inner: 0 })?;
97//!
98//!     // We borrow the guard and then dereference
99//!     // it to get a mutable reference to Number
100//!     let mut guard: PyRefMut<'_, Number> = n.bind(py).borrow_mut();
101//!     let n_mutable: &mut Number = &mut *guard;
102//!
103//!     n_mutable.increment();
104//!
105//!     // To avoid panics we must dispose of the
106//!     // `PyRefMut` before borrowing again.
107//!     drop(guard);
108//!
109//!     let n_immutable: &Number = &n.bind(py).borrow();
110//!     assert_eq!(n_immutable.inner, 1);
111//!
112//!     Ok(())
113//! })
114//! # }
115//! ```
116//! ## Dealing with possibly overlapping mutable references
117//!
118//! It is also necessary to use `PyCell` if you can receive mutable arguments that may overlap.
119//! Suppose the following function that swaps the values of two `Number`s:
120//! ```
121//! # use pyo3::prelude::*;
122//! # #[pyclass]
123//! # pub struct Number {
124//! #     inner: u32,
125//! # }
126//! #[pyfunction]
127//! fn swap_numbers(a: &mut Number, b: &mut Number) {
128//!     std::mem::swap(&mut a.inner, &mut b.inner);
129//! }
130//! # fn main() {
131//! #     Python::with_gil(|py| {
132//! #         let n = Py::new(py, Number{inner: 35}).unwrap();
133//! #         let n2 = n.clone_ref(py);
134//! #         assert!(n.is(&n2));
135//! #         let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
136//! #         fun.call1((n, n2)).expect_err("Managed to create overlapping mutable references. Note: this is undefined behaviour.");
137//! #     });
138//! # }
139//! ```
140//! When users pass in the same `Number` as both arguments, one of the mutable borrows will
141//! fail and raise a `RuntimeError`:
142//! ```text
143//! >>> a = Number()
144//! >>> swap_numbers(a, a)
145//! Traceback (most recent call last):
146//!   File "<stdin>", line 1, in <module>
147//!   RuntimeError: Already borrowed
148//! ```
149//!
150//! It is better to write that function like this:
151//! ```rust,ignore
152//! # #![allow(deprecated)]
153//! # use pyo3::prelude::*;
154//! # #[pyclass]
155//! # pub struct Number {
156//! #     inner: u32,
157//! # }
158//! #[pyfunction]
159//! fn swap_numbers(a: &PyCell<Number>, b: &PyCell<Number>) {
160//!     // Check that the pointers are unequal
161//!     if !a.is(b) {
162//!         std::mem::swap(&mut a.borrow_mut().inner, &mut b.borrow_mut().inner);
163//!     } else {
164//!         // Do nothing - they are the same object, so don't need swapping.
165//!     }
166//! }
167//! # fn main() {
168//! #     // With duplicate numbers
169//! #     Python::with_gil(|py| {
170//! #         let n = Py::new(py, Number{inner: 35}).unwrap();
171//! #         let n2 = n.clone_ref(py);
172//! #         assert!(n.is(&n2));
173//! #         let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
174//! #         fun.call1((n, n2)).unwrap();
175//! #     });
176//! #
177//! #     // With two different numbers
178//! #     Python::with_gil(|py| {
179//! #         let n = Py::new(py, Number{inner: 35}).unwrap();
180//! #         let n2 = Py::new(py, Number{inner: 42}).unwrap();
181//! #         assert!(!n.is(&n2));
182//! #         let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
183//! #         fun.call1((&n, &n2)).unwrap();
184//! #         let n: u32 = n.borrow(py).inner;
185//! #         let n2: u32 = n2.borrow(py).inner;
186//! #         assert_eq!(n, 42);
187//! #         assert_eq!(n2, 35);
188//! #     });
189//! # }
190//! ```
191//! See the [guide] for more information.
192//!
193//! [guide]: https://pyo3.rs/latest/class.html#pycell-and-interior-mutability "PyCell and interior mutability"
194//! [Interior Mutability]: https://doc.rust-lang.org/book/ch15-05-interior-mutability.html "RefCell<T> and the Interior Mutability Pattern - The Rust Programming Language"
195
196use crate::conversion::IntoPyObject;
197use crate::exceptions::PyRuntimeError;
198use crate::ffi_ptr_ext::FfiPtrExt;
199use crate::internal_tricks::{ptr_from_mut, ptr_from_ref};
200use crate::pyclass::{boolean_struct::False, PyClass};
201use crate::types::any::PyAnyMethods;
202use crate::{ffi, Borrowed, Bound, PyErr, Python};
203use std::convert::Infallible;
204use std::fmt;
205use std::mem::ManuallyDrop;
206use std::ops::{Deref, DerefMut};
207
208pub(crate) mod impl_;
209use impl_::{PyClassBorrowChecker, PyClassObjectLayout};
210
211/// A wrapper type for an immutably borrowed value from a [`Bound<'py, T>`].
212///
213/// See the [`Bound`] documentation for more information.
214///
215/// # Examples
216///
217/// You can use [`PyRef`] as an alternative to a `&self` receiver when
218/// - you need to access the pointer of the [`Bound`], or
219/// - you want to get a super class.
220/// ```
221/// # use pyo3::prelude::*;
222/// #[pyclass(subclass)]
223/// struct Parent {
224///     basename: &'static str,
225/// }
226///
227/// #[pyclass(extends=Parent)]
228/// struct Child {
229///     name: &'static str,
230///  }
231///
232/// #[pymethods]
233/// impl Child {
234///     #[new]
235///     fn new() -> (Self, Parent) {
236///         (Child { name: "Caterpillar" }, Parent { basename: "Butterfly" })
237///     }
238///
239///     fn format(slf: PyRef<'_, Self>) -> String {
240///         // We can get *mut ffi::PyObject from PyRef
241///         let refcnt = unsafe { pyo3::ffi::Py_REFCNT(slf.as_ptr()) };
242///         // We can get &Self::BaseType by as_ref
243///         let basename = slf.as_ref().basename;
244///         format!("{}(base: {}, cnt: {})", slf.name, basename, refcnt)
245///     }
246/// }
247/// # Python::with_gil(|py| {
248/// #     let sub = Py::new(py, Child::new()).unwrap();
249/// #     pyo3::py_run!(py, sub, "assert sub.format() == 'Caterpillar(base: Butterfly, cnt: 4)', sub.format()");
250/// # });
251/// ```
252///
253/// See the [module-level documentation](self) for more information.
254#[repr(transparent)]
255pub struct PyRef<'p, T: PyClass> {
256    // TODO: once the GIL Ref API is removed, consider adding a lifetime parameter to `PyRef` to
257    // store `Borrowed` here instead, avoiding reference counting overhead.
258    inner: Bound<'p, T>,
259}
260
261impl<'p, T: PyClass> PyRef<'p, T> {
262    /// Returns a `Python` token that is bound to the lifetime of the `PyRef`.
263    pub fn py(&self) -> Python<'p> {
264        self.inner.py()
265    }
266}
267
268impl<T, U> AsRef<U> for PyRef<'_, T>
269where
270    T: PyClass<BaseType = U>,
271    U: PyClass,
272{
273    fn as_ref(&self) -> &T::BaseType {
274        self.as_super()
275    }
276}
277
278impl<'py, T: PyClass> PyRef<'py, T> {
279    /// Returns the raw FFI pointer represented by self.
280    ///
281    /// # Safety
282    ///
283    /// Callers are responsible for ensuring that the pointer does not outlive self.
284    ///
285    /// The reference is borrowed; callers should not decrease the reference count
286    /// when they are finished with the pointer.
287    #[inline]
288    pub fn as_ptr(&self) -> *mut ffi::PyObject {
289        self.inner.as_ptr()
290    }
291
292    /// Returns an owned raw FFI pointer represented by self.
293    ///
294    /// # Safety
295    ///
296    /// The reference is owned; when finished the caller should either transfer ownership
297    /// of the pointer or decrease the reference count (e.g. with [`pyo3::ffi::Py_DecRef`](crate::ffi::Py_DecRef)).
298    #[inline]
299    pub fn into_ptr(self) -> *mut ffi::PyObject {
300        self.inner.clone().into_ptr()
301    }
302
303    #[track_caller]
304    pub(crate) fn borrow(obj: &Bound<'py, T>) -> Self {
305        Self::try_borrow(obj).expect("Already mutably borrowed")
306    }
307
308    pub(crate) fn try_borrow(obj: &Bound<'py, T>) -> Result<Self, PyBorrowError> {
309        let cell = obj.get_class_object();
310        cell.ensure_threadsafe();
311        cell.borrow_checker()
312            .try_borrow()
313            .map(|_| Self { inner: obj.clone() })
314    }
315}
316
317impl<'p, T, U> PyRef<'p, T>
318where
319    T: PyClass<BaseType = U>,
320    U: PyClass,
321{
322    /// Gets a `PyRef<T::BaseType>`.
323    ///
324    /// While `as_ref()` returns a reference of type `&T::BaseType`, this cannot be
325    /// used to get the base of `T::BaseType`.
326    ///
327    /// But with the help of this method, you can get hold of instances of the
328    /// super-superclass when needed.
329    ///
330    /// # Examples
331    /// ```
332    /// # use pyo3::prelude::*;
333    /// #[pyclass(subclass)]
334    /// struct Base1 {
335    ///     name1: &'static str,
336    /// }
337    ///
338    /// #[pyclass(extends=Base1, subclass)]
339    /// struct Base2 {
340    ///     name2: &'static str,
341    /// }
342    ///
343    /// #[pyclass(extends=Base2)]
344    /// struct Sub {
345    ///     name3: &'static str,
346    /// }
347    ///
348    /// #[pymethods]
349    /// impl Sub {
350    ///     #[new]
351    ///     fn new() -> PyClassInitializer<Self> {
352    ///         PyClassInitializer::from(Base1 { name1: "base1" })
353    ///             .add_subclass(Base2 { name2: "base2" })
354    ///             .add_subclass(Self { name3: "sub" })
355    ///     }
356    ///     fn name(slf: PyRef<'_, Self>) -> String {
357    ///         let subname = slf.name3;
358    ///         let super_ = slf.into_super();
359    ///         format!("{} {} {}", super_.as_ref().name1, super_.name2, subname)
360    ///     }
361    /// }
362    /// # Python::with_gil(|py| {
363    /// #     let sub = Py::new(py, Sub::new()).unwrap();
364    /// #     pyo3::py_run!(py, sub, "assert sub.name() == 'base1 base2 sub'")
365    /// # });
366    /// ```
367    pub fn into_super(self) -> PyRef<'p, U> {
368        let py = self.py();
369        PyRef {
370            inner: unsafe {
371                ManuallyDrop::new(self)
372                    .as_ptr()
373                    .assume_owned_unchecked(py)
374                    .downcast_into_unchecked()
375            },
376        }
377    }
378
379    /// Borrows a shared reference to `PyRef<T::BaseType>`.
380    ///
381    /// With the help of this method, you can access attributes and call methods
382    /// on the superclass without consuming the `PyRef<T>`. This method can also
383    /// be chained to access the super-superclass (and so on).
384    ///
385    /// # Examples
386    /// ```
387    /// # use pyo3::prelude::*;
388    /// #[pyclass(subclass)]
389    /// struct Base {
390    ///     base_name: &'static str,
391    /// }
392    /// #[pymethods]
393    /// impl Base {
394    ///     fn base_name_len(&self) -> usize {
395    ///         self.base_name.len()
396    ///     }
397    /// }
398    ///
399    /// #[pyclass(extends=Base)]
400    /// struct Sub {
401    ///     sub_name: &'static str,
402    /// }
403    ///
404    /// #[pymethods]
405    /// impl Sub {
406    ///     #[new]
407    ///     fn new() -> (Self, Base) {
408    ///         (Self { sub_name: "sub_name" }, Base { base_name: "base_name" })
409    ///     }
410    ///     fn sub_name_len(&self) -> usize {
411    ///         self.sub_name.len()
412    ///     }
413    ///     fn format_name_lengths(slf: PyRef<'_, Self>) -> String {
414    ///         format!("{} {}", slf.as_super().base_name_len(), slf.sub_name_len())
415    ///     }
416    /// }
417    /// # Python::with_gil(|py| {
418    /// #     let sub = Py::new(py, Sub::new()).unwrap();
419    /// #     pyo3::py_run!(py, sub, "assert sub.format_name_lengths() == '9 8'")
420    /// # });
421    /// ```
422    pub fn as_super(&self) -> &PyRef<'p, U> {
423        let ptr = ptr_from_ref::<Bound<'p, T>>(&self.inner)
424            // `Bound<T>` has the same layout as `Bound<T::BaseType>`
425            .cast::<Bound<'p, T::BaseType>>()
426            // `Bound<T::BaseType>` has the same layout as `PyRef<T::BaseType>`
427            .cast::<PyRef<'p, T::BaseType>>();
428        unsafe { &*ptr }
429    }
430}
431
432impl<T: PyClass> Deref for PyRef<'_, T> {
433    type Target = T;
434
435    #[inline]
436    fn deref(&self) -> &T {
437        unsafe { &*self.inner.get_class_object().get_ptr() }
438    }
439}
440
441impl<T: PyClass> Drop for PyRef<'_, T> {
442    fn drop(&mut self) {
443        self.inner
444            .get_class_object()
445            .borrow_checker()
446            .release_borrow()
447    }
448}
449
450impl<'py, T: PyClass> IntoPyObject<'py> for PyRef<'py, T> {
451    type Target = T;
452    type Output = Bound<'py, T>;
453    type Error = Infallible;
454
455    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
456        Ok(self.inner.clone())
457    }
458}
459
460impl<'a, 'py, T: PyClass> IntoPyObject<'py> for &'a PyRef<'py, T> {
461    type Target = T;
462    type Output = Borrowed<'a, 'py, T>;
463    type Error = Infallible;
464
465    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
466        Ok(self.inner.as_borrowed())
467    }
468}
469
470impl<T: PyClass + fmt::Debug> fmt::Debug for PyRef<'_, T> {
471    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
472        fmt::Debug::fmt(&**self, f)
473    }
474}
475
476/// A wrapper type for a mutably borrowed value from a [`Bound<'py, T>`].
477///
478/// See the [module-level documentation](self) for more information.
479#[repr(transparent)]
480pub struct PyRefMut<'p, T: PyClass<Frozen = False>> {
481    // TODO: once the GIL Ref API is removed, consider adding a lifetime parameter to `PyRef` to
482    // store `Borrowed` here instead, avoiding reference counting overhead.
483    inner: Bound<'p, T>,
484}
485
486impl<'p, T: PyClass<Frozen = False>> PyRefMut<'p, T> {
487    /// Returns a `Python` token that is bound to the lifetime of the `PyRefMut`.
488    pub fn py(&self) -> Python<'p> {
489        self.inner.py()
490    }
491}
492
493impl<T, U> AsRef<U> for PyRefMut<'_, T>
494where
495    T: PyClass<BaseType = U, Frozen = False>,
496    U: PyClass<Frozen = False>,
497{
498    fn as_ref(&self) -> &T::BaseType {
499        PyRefMut::downgrade(self).as_super()
500    }
501}
502
503impl<T, U> AsMut<U> for PyRefMut<'_, T>
504where
505    T: PyClass<BaseType = U, Frozen = False>,
506    U: PyClass<Frozen = False>,
507{
508    fn as_mut(&mut self) -> &mut T::BaseType {
509        self.as_super()
510    }
511}
512
513impl<'py, T: PyClass<Frozen = False>> PyRefMut<'py, T> {
514    /// Returns the raw FFI pointer represented by self.
515    ///
516    /// # Safety
517    ///
518    /// Callers are responsible for ensuring that the pointer does not outlive self.
519    ///
520    /// The reference is borrowed; callers should not decrease the reference count
521    /// when they are finished with the pointer.
522    #[inline]
523    pub fn as_ptr(&self) -> *mut ffi::PyObject {
524        self.inner.as_ptr()
525    }
526
527    /// Returns an owned raw FFI pointer represented by self.
528    ///
529    /// # Safety
530    ///
531    /// The reference is owned; when finished the caller should either transfer ownership
532    /// of the pointer or decrease the reference count (e.g. with [`pyo3::ffi::Py_DecRef`](crate::ffi::Py_DecRef)).
533    #[inline]
534    pub fn into_ptr(self) -> *mut ffi::PyObject {
535        self.inner.clone().into_ptr()
536    }
537
538    #[inline]
539    #[track_caller]
540    pub(crate) fn borrow(obj: &Bound<'py, T>) -> Self {
541        Self::try_borrow(obj).expect("Already borrowed")
542    }
543
544    pub(crate) fn try_borrow(obj: &Bound<'py, T>) -> Result<Self, PyBorrowMutError> {
545        let cell = obj.get_class_object();
546        cell.ensure_threadsafe();
547        cell.borrow_checker()
548            .try_borrow_mut()
549            .map(|_| Self { inner: obj.clone() })
550    }
551
552    pub(crate) fn downgrade(slf: &Self) -> &PyRef<'py, T> {
553        // `PyRefMut<T>` and `PyRef<T>` have the same layout
554        unsafe { &*ptr_from_ref(slf).cast() }
555    }
556}
557
558impl<'p, T, U> PyRefMut<'p, T>
559where
560    T: PyClass<BaseType = U, Frozen = False>,
561    U: PyClass<Frozen = False>,
562{
563    /// Gets a `PyRef<T::BaseType>`.
564    ///
565    /// See [`PyRef::into_super`] for more.
566    pub fn into_super(self) -> PyRefMut<'p, U> {
567        let py = self.py();
568        PyRefMut {
569            inner: unsafe {
570                ManuallyDrop::new(self)
571                    .as_ptr()
572                    .assume_owned_unchecked(py)
573                    .downcast_into_unchecked()
574            },
575        }
576    }
577
578    /// Borrows a mutable reference to `PyRefMut<T::BaseType>`.
579    ///
580    /// With the help of this method, you can mutate attributes and call mutating
581    /// methods on the superclass without consuming the `PyRefMut<T>`. This method
582    /// can also be chained to access the super-superclass (and so on).
583    ///
584    /// See [`PyRef::as_super`] for more.
585    pub fn as_super(&mut self) -> &mut PyRefMut<'p, U> {
586        let ptr = ptr_from_mut::<Bound<'p, T>>(&mut self.inner)
587            // `Bound<T>` has the same layout as `Bound<T::BaseType>`
588            .cast::<Bound<'p, T::BaseType>>()
589            // `Bound<T::BaseType>` has the same layout as `PyRefMut<T::BaseType>`,
590            // and the mutable borrow on `self` prevents aliasing
591            .cast::<PyRefMut<'p, T::BaseType>>();
592        unsafe { &mut *ptr }
593    }
594}
595
596impl<T: PyClass<Frozen = False>> Deref for PyRefMut<'_, T> {
597    type Target = T;
598
599    #[inline]
600    fn deref(&self) -> &T {
601        unsafe { &*self.inner.get_class_object().get_ptr() }
602    }
603}
604
605impl<T: PyClass<Frozen = False>> DerefMut for PyRefMut<'_, T> {
606    #[inline]
607    fn deref_mut(&mut self) -> &mut T {
608        unsafe { &mut *self.inner.get_class_object().get_ptr() }
609    }
610}
611
612impl<T: PyClass<Frozen = False>> Drop for PyRefMut<'_, T> {
613    fn drop(&mut self) {
614        self.inner
615            .get_class_object()
616            .borrow_checker()
617            .release_borrow_mut()
618    }
619}
620
621impl<'py, T: PyClass<Frozen = False>> IntoPyObject<'py> for PyRefMut<'py, T> {
622    type Target = T;
623    type Output = Bound<'py, T>;
624    type Error = Infallible;
625
626    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
627        Ok(self.inner.clone())
628    }
629}
630
631impl<'a, 'py, T: PyClass<Frozen = False>> IntoPyObject<'py> for &'a PyRefMut<'py, T> {
632    type Target = T;
633    type Output = Borrowed<'a, 'py, T>;
634    type Error = Infallible;
635
636    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
637        Ok(self.inner.as_borrowed())
638    }
639}
640
641impl<T: PyClass<Frozen = False> + fmt::Debug> fmt::Debug for PyRefMut<'_, T> {
642    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
643        fmt::Debug::fmt(self.deref(), f)
644    }
645}
646
647/// An error type returned by [`Bound::try_borrow`].
648///
649/// If this error is allowed to bubble up into Python code it will raise a `RuntimeError`.
650pub struct PyBorrowError {
651    _private: (),
652}
653
654impl fmt::Debug for PyBorrowError {
655    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
656        f.debug_struct("PyBorrowError").finish()
657    }
658}
659
660impl fmt::Display for PyBorrowError {
661    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
662        fmt::Display::fmt("Already mutably borrowed", f)
663    }
664}
665
666impl From<PyBorrowError> for PyErr {
667    fn from(other: PyBorrowError) -> Self {
668        PyRuntimeError::new_err(other.to_string())
669    }
670}
671
672/// An error type returned by [`Bound::try_borrow_mut`].
673///
674/// If this error is allowed to bubble up into Python code it will raise a `RuntimeError`.
675pub struct PyBorrowMutError {
676    _private: (),
677}
678
679impl fmt::Debug for PyBorrowMutError {
680    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
681        f.debug_struct("PyBorrowMutError").finish()
682    }
683}
684
685impl fmt::Display for PyBorrowMutError {
686    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
687        fmt::Display::fmt("Already borrowed", f)
688    }
689}
690
691impl From<PyBorrowMutError> for PyErr {
692    fn from(other: PyBorrowMutError) -> Self {
693        PyRuntimeError::new_err(other.to_string())
694    }
695}
696
697#[cfg(test)]
698#[cfg(feature = "macros")]
699mod tests {
700
701    use super::*;
702
703    #[crate::pyclass]
704    #[pyo3(crate = "crate")]
705    #[derive(Copy, Clone, PartialEq, Eq, Debug)]
706    struct SomeClass(i32);
707
708    #[test]
709    fn test_as_ptr() {
710        Python::with_gil(|py| {
711            let cell = Bound::new(py, SomeClass(0)).unwrap();
712            let ptr = cell.as_ptr();
713
714            assert_eq!(cell.borrow().as_ptr(), ptr);
715            assert_eq!(cell.borrow_mut().as_ptr(), ptr);
716        })
717    }
718
719    #[test]
720    fn test_into_ptr() {
721        Python::with_gil(|py| {
722            let cell = Bound::new(py, SomeClass(0)).unwrap();
723            let ptr = cell.as_ptr();
724
725            assert_eq!(cell.borrow().into_ptr(), ptr);
726            unsafe { ffi::Py_DECREF(ptr) };
727
728            assert_eq!(cell.borrow_mut().into_ptr(), ptr);
729            unsafe { ffi::Py_DECREF(ptr) };
730        })
731    }
732
733    #[crate::pyclass]
734    #[pyo3(crate = "crate", subclass)]
735    struct BaseClass {
736        val1: usize,
737    }
738
739    #[crate::pyclass]
740    #[pyo3(crate = "crate", extends=BaseClass, subclass)]
741    struct SubClass {
742        val2: usize,
743    }
744
745    #[crate::pyclass]
746    #[pyo3(crate = "crate", extends=SubClass)]
747    struct SubSubClass {
748        val3: usize,
749    }
750
751    #[crate::pymethods]
752    #[pyo3(crate = "crate")]
753    impl SubSubClass {
754        #[new]
755        fn new(py: Python<'_>) -> crate::Py<SubSubClass> {
756            let init = crate::PyClassInitializer::from(BaseClass { val1: 10 })
757                .add_subclass(SubClass { val2: 15 })
758                .add_subclass(SubSubClass { val3: 20 });
759            crate::Py::new(py, init).expect("allocation error")
760        }
761
762        fn get_values(self_: PyRef<'_, Self>) -> (usize, usize, usize) {
763            let val1 = self_.as_super().as_super().val1;
764            let val2 = self_.as_super().val2;
765            (val1, val2, self_.val3)
766        }
767
768        fn double_values(mut self_: PyRefMut<'_, Self>) {
769            self_.as_super().as_super().val1 *= 2;
770            self_.as_super().val2 *= 2;
771            self_.val3 *= 2;
772        }
773    }
774
775    #[test]
776    fn test_pyref_as_super() {
777        Python::with_gil(|py| {
778            let obj = SubSubClass::new(py).into_bound(py);
779            let pyref = obj.borrow();
780            assert_eq!(pyref.as_super().as_super().val1, 10);
781            assert_eq!(pyref.as_super().val2, 15);
782            assert_eq!(pyref.as_ref().val2, 15); // `as_ref` also works
783            assert_eq!(pyref.val3, 20);
784            assert_eq!(SubSubClass::get_values(pyref), (10, 15, 20));
785        });
786    }
787
788    #[test]
789    fn test_pyrefmut_as_super() {
790        Python::with_gil(|py| {
791            let obj = SubSubClass::new(py).into_bound(py);
792            assert_eq!(SubSubClass::get_values(obj.borrow()), (10, 15, 20));
793            {
794                let mut pyrefmut = obj.borrow_mut();
795                assert_eq!(pyrefmut.as_super().as_ref().val1, 10);
796                pyrefmut.as_super().as_super().val1 -= 5;
797                pyrefmut.as_super().val2 -= 3;
798                pyrefmut.as_mut().val2 -= 2; // `as_mut` also works
799                pyrefmut.val3 -= 5;
800            }
801            assert_eq!(SubSubClass::get_values(obj.borrow()), (5, 10, 15));
802            SubSubClass::double_values(obj.borrow_mut());
803            assert_eq!(SubSubClass::get_values(obj.borrow()), (10, 20, 30));
804        });
805    }
806
807    #[test]
808    fn test_pyrefs_in_python() {
809        Python::with_gil(|py| {
810            let obj = SubSubClass::new(py);
811            crate::py_run!(py, obj, "assert obj.get_values() == (10, 15, 20)");
812            crate::py_run!(py, obj, "assert obj.double_values() is None");
813            crate::py_run!(py, obj, "assert obj.get_values() == (20, 30, 40)");
814        });
815    }
816}
⚠️ Internal Docs ⚠️ Not Public API 👉 Official Docs Here