# conversion.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/pyo3-0.13.2/src/conversion.rs`.
Keywords: rust, rustlang, rust-lang

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    // Copyright (c) 2017-present PyO3 Project and Contributors

    //! Conversions between various states of Rust and Python types and their wrappers.
    use crate::err::{self, PyDowncastError, PyResult};
    use crate::type_object::PyTypeInfo;
    use crate::types::PyTuple;
    use crate::{
        ffi, gil, Py, PyAny, PyCell, PyClass, PyNativeType, PyObject, PyRef, PyRefMut, Python,
    };
    use std::ptr::NonNull;

    /// This trait represents that **we can do zero-cost conversion from the object
    /// to a FFI pointer**.
    ///
    /// This trait is implemented for types that internally wrap a pointer to a Python object.
    ///
    /// # Example
    ///
    /// ```
    /// use pyo3::{AsPyPointer, prelude::*};
    /// let gil = Python::acquire_gil();
    /// let dict = pyo3::types::PyDict::new(gil.python());
    /// // All native object wrappers implement AsPyPointer!!!
    /// assert_ne!(dict.as_ptr(), std::ptr::null_mut());
    /// ```
    pub trait AsPyPointer {
        /// Retrieves the underlying FFI pointer (as a borrowed pointer).
        fn as_ptr(&self) -> *mut ffi::PyObject;
    }

    /// This trait allows retrieving the underlying FFI pointer from Python objects.
    pub trait IntoPyPointer {
        /// Retrieves the underlying FFI pointer. Whether pointer owned or borrowed
        /// depends on implementation.
        fn into_ptr(self) -> *mut ffi::PyObject;
    }

    /// Convert `None` into a null pointer.
    impl<T> AsPyPointer for Option<T>
    where
        T: AsPyPointer,
    {
        #[inline]
        fn as_ptr(&self) -> *mut ffi::PyObject {
            self.as_ref()
                .map_or_else(std::ptr::null_mut, |t| t.into_ptr())
        }
    }

    /// Convert `None` into a null pointer.
    impl<T> IntoPyPointer for Option<T>
    where
        T: IntoPyPointer,
    {
        #[inline]
        fn into_ptr(self) -> *mut ffi::PyObject {
            self.map_or_else(std::ptr::null_mut, |t| t.into_ptr())
        }
    }

    impl<'a, T> IntoPyPointer for &'a T
    where
        T: AsPyPointer,
    {
        fn into_ptr(self) -> *mut ffi::PyObject {
            let ptr = self.as_ptr();
            if !ptr.is_null() {
                unsafe {
                    ffi::Py_INCREF(ptr);
                }
            }
            ptr
        }
    }

    /// Conversion trait that allows various objects to be converted into `PyObject`.
    pub trait ToPyObject {
        /// Converts self into a Python object.
        fn to_object(&self, py: Python) -> PyObject;
    }

    /// This trait has two implementations: The slow one is implemented for
    /// all [ToPyObject] and creates a new object using [ToPyObject::to_object],
    /// while the fast one is only implemented for AsPyPointer (we know
    /// that every AsPyPointer is also ToPyObject) and uses [AsPyPointer::as_ptr()]
    pub trait ToBorrowedObject: ToPyObject {
        /// Converts self into a Python object and calls the specified closure
        /// on the native FFI pointer underlying the Python object.
        ///
        /// May be more efficient than `to_object` because it does not need
        /// to touch any reference counts when the input object already is a Python object.
        fn with_borrowed_ptr<F, R>(&self, py: Python, f: F) -> R
        where
            F: FnOnce(*mut ffi::PyObject) -> R,
        {
            let ptr = self.to_object(py).into_ptr();
            let result = f(ptr);
            unsafe {
                ffi::Py_XDECREF(ptr);
            }
            result
        }
    }

    impl<T> ToBorrowedObject for T
    where
        T: ToPyObject,
    {
        #[cfg(feature = "nightly")]
        default fn with_borrowed_ptr<F, R>(&self, py: Python, f: F) -> R
        where
            F: FnOnce(*mut ffi::PyObject) -> R,
        {
            let ptr = self.to_object(py).into_ptr();
            let result = f(ptr);
            unsafe {
                ffi::Py_XDECREF(ptr);
            }
            result
        }
    }

    #[cfg(feature = "nightly")]
    impl<T> ToBorrowedObject for T
    where
        T: ToPyObject + AsPyPointer,
    {
        fn with_borrowed_ptr<F, R>(&self, _py: Python, f: F) -> R
        where
            F: FnOnce(*mut ffi::PyObject) -> R,
        {
            f(self.as_ptr())
        }
    }

    /// Similar to [std::convert::Into], just that it requires a gil token.
    ///
    /// `IntoPy<PyObject>` (aka `IntoPy<Py<PyAny>>`) should be implemented to define a conversion from
    /// Rust to Python which can be used by most of PyO3's methods.
    pub trait IntoPy<T>: Sized {
        /// Performs the conversion.
        fn into_py(self, py: Python) -> T;
    }

    /// `FromPyObject` is implemented by various types that can be extracted from
    /// a Python object reference.
    ///
    /// Normal usage is through the helper methods `Py::extract` or `PyAny::extract`:
    ///
    /// ```rust,ignore
    /// let obj: Py<PyAny> = ...;
    /// let value: &TargetType = obj.extract(py)?;
    ///
    /// let any: &PyAny = ...;
    /// let value: &TargetType = any.extract()?;
    /// ```
    ///
    /// Note: depending on the implementation, the lifetime of the extracted result may
    /// depend on the lifetime of the `obj` or the `prepared` variable.
    ///
    /// For example, when extracting `&str` from a Python byte string, the resulting string slice will
    /// point to the existing string data (lifetime: `'source`).
    /// On the other hand, when extracting `&str` from a Python Unicode string, the preparation step
    /// will convert the string to UTF-8, and the resulting string slice will have lifetime `'prepared`.
    /// Since which case applies depends on the runtime type of the Python object,
    /// both the `obj` and `prepared` variables must outlive the resulting string slice.
    ///
    /// The trait's conversion method takes a `&PyAny` argument but is called
    /// `FromPyObject` for historical reasons.
    pub trait FromPyObject<'source>: Sized {
        /// Extracts `Self` from the source `PyObject`.
        fn extract(ob: &'source PyAny) -> PyResult<Self>;
    }

    /// Identity conversion: allows using existing `PyObject` instances where
    /// `T: ToPyObject` is expected.
    impl<T: ?Sized + ToPyObject> ToPyObject for &'_ T {
        #[inline]
        fn to_object(&self, py: Python) -> PyObject {
            <T as ToPyObject>::to_object(*self, py)
        }
    }

    /// `Option::Some<T>` is converted like `T`.
    /// `Option::None` is converted to Python `None`.
    impl<T> ToPyObject for Option<T>
    where
        T: ToPyObject,
    {
        fn to_object(&self, py: Python) -> PyObject {
            self.as_ref()
                .map_or_else(|| py.None(), |val| val.to_object(py))
        }
    }

    impl<T> IntoPy<PyObject> for Option<T>
    where
        T: IntoPy<PyObject>,
    {
        fn into_py(self, py: Python) -> PyObject {
            self.map_or_else(|| py.None(), |val| val.into_py(py))
        }
    }

    /// `()` is converted to Python `None`.
    impl ToPyObject for () {
        fn to_object(&self, py: Python) -> PyObject {
            py.None()
        }
    }

    impl IntoPy<PyObject> for () {
        fn into_py(self, py: Python) -> PyObject {
            py.None()
        }
    }

    impl<T> IntoPy<PyObject> for &'_ T
    where
        T: AsPyPointer,
    {
        #[inline]
        fn into_py(self, py: Python) -> PyObject {
            unsafe { PyObject::from_borrowed_ptr(py, self.as_ptr()) }
        }
    }

    impl<'a, T> FromPyObject<'a> for &'a PyCell<T>
    where
        T: PyClass,
    {
        fn extract(obj: &'a PyAny) -> PyResult<Self> {
            PyTryFrom::try_from(obj).map_err(Into::into)
        }
    }

    impl<'a, T> FromPyObject<'a> for T
    where
        T: PyClass + Clone,
    {
        fn extract(obj: &'a PyAny) -> PyResult<Self> {
            let cell: &PyCell<Self> = PyTryFrom::try_from(obj)?;
            Ok(unsafe { cell.try_borrow_unguarded()?.clone() })
        }
    }

    impl<'a, T> FromPyObject<'a> for PyRef<'a, T>
    where
        T: PyClass,
    {
        fn extract(obj: &'a PyAny) -> PyResult<Self> {
            let cell: &PyCell<T> = PyTryFrom::try_from(obj)?;
            cell.try_borrow().map_err(Into::into)
        }
    }

    impl<'a, T> FromPyObject<'a> for PyRefMut<'a, T>
    where
        T: PyClass,
    {
        fn extract(obj: &'a PyAny) -> PyResult<Self> {
            let cell: &PyCell<T> = PyTryFrom::try_from(obj)?;
            cell.try_borrow_mut().map_err(Into::into)
        }
    }

    impl<'a, T> FromPyObject<'a> for Option<T>
    where
        T: FromPyObject<'a>,
    {
        fn extract(obj: &'a PyAny) -> PyResult<Self> {
            if obj.as_ptr() == unsafe { ffi::Py_None() } {
                Ok(None)
            } else {
                T::extract(obj).map(Some)
            }
        }
    }

    /// Trait implemented by Python object types that allow a checked downcast.
    /// If `T` implements `PyTryFrom`, we can convert `&PyAny` to `&T`.
    ///
    /// This trait is similar to `std::convert::TryFrom`
    pub trait PyTryFrom<'v>: Sized + PyNativeType {
        /// Cast from a concrete Python object type to PyObject.
        fn try_from<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>>;

        /// Cast from a concrete Python object type to PyObject. With exact type check.
        fn try_from_exact<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>>;

        /// Cast a PyAny to a specific type of PyObject. The caller must
        /// have already verified the reference is for this type.
        ///
        /// # Safety
        ///
        /// Callers must ensure that the type is valid or risk type confusion.
        unsafe fn try_from_unchecked<V: Into<&'v PyAny>>(value: V) -> &'v Self;
    }

    /// Trait implemented by Python object types that allow a checked downcast.
    /// This trait is similar to `std::convert::TryInto`
    pub trait PyTryInto<T>: Sized {
        /// Cast from PyObject to a concrete Python object type.
        fn try_into(&self) -> Result<&T, PyDowncastError>;

        /// Cast from PyObject to a concrete Python object type. With exact type check.
        fn try_into_exact(&self) -> Result<&T, PyDowncastError>;
    }

    // TryFrom implies TryInto
    impl<U> PyTryInto<U> for PyAny
    where
        U: for<'v> PyTryFrom<'v>,
    {
        fn try_into(&self) -> Result<&U, PyDowncastError> {
            U::try_from(self)
        }
        fn try_into_exact(&self) -> Result<&U, PyDowncastError> {
            U::try_from_exact(self)
        }
    }

    impl<'v, T> PyTryFrom<'v> for T
    where
        T: PyTypeInfo + PyNativeType,
    {
        fn try_from<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>> {
            let value = value.into();
            unsafe {
                if T::is_type_of(value) {
                    Ok(Self::try_from_unchecked(value))
                } else {
                    Err(PyDowncastError::new(value, T::NAME))
                }
            }
        }

        fn try_from_exact<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>> {
            let value = value.into();
            unsafe {
                if T::is_exact_type_of(value) {
                    Ok(Self::try_from_unchecked(value))
                } else {
                    Err(PyDowncastError::new(value, T::NAME))
                }
            }
        }

        #[inline]
        unsafe fn try_from_unchecked<V: Into<&'v PyAny>>(value: V) -> &'v Self {
            Self::unchecked_downcast(value.into())
        }
    }

    impl<'v, T> PyTryFrom<'v> for PyCell<T>
    where
        T: 'v + PyClass,
    {
        fn try_from<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>> {
            let value = value.into();
            unsafe {
                if T::is_type_of(value) {
                    Ok(Self::try_from_unchecked(value))
                } else {
                    Err(PyDowncastError::new(value, T::NAME))
                }
            }
        }
        fn try_from_exact<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>> {
            let value = value.into();
            unsafe {
                if T::is_exact_type_of(value) {
                    Ok(Self::try_from_unchecked(value))
                } else {
                    Err(PyDowncastError::new(value, T::NAME))
                }
            }
        }
        #[inline]
        unsafe fn try_from_unchecked<V: Into<&'v PyAny>>(value: V) -> &'v Self {
            Self::unchecked_downcast(value.into())
        }
    }

    /// Converts `()` to an empty Python tuple.
    impl IntoPy<Py<PyTuple>> for () {
        fn into_py(self, py: Python) -> Py<PyTuple> {
            PyTuple::empty(py).into()
        }
    }

    /// Raw level conversion between `*mut ffi::PyObject` and PyO3 types.
    pub unsafe trait FromPyPointer<'p>: Sized {
        /// Convert from an arbitrary `PyObject`.
        ///
        /// # Safety
        ///
        /// Implementations must ensure the object does not get freed during `'p`
        /// and ensure that `ptr` is of the correct type.
        /// Note that it must be safe to decrement the reference count of `ptr`.
        unsafe fn from_owned_ptr_or_opt(py: Python<'p>, ptr: *mut ffi::PyObject) -> Option<&'p Self>;
        /// Convert from an arbitrary `PyObject` or panic.
        ///
        /// # Safety
        ///
        /// Relies on [`from_owned_ptr_or_opt`](#method.from_owned_ptr_or_opt).
        unsafe fn from_owned_ptr_or_panic(py: Python<'p>, ptr: *mut ffi::PyObject) -> &'p Self {
            Self::from_owned_ptr_or_opt(py, ptr).unwrap_or_else(|| err::panic_after_error(py))
        }
        /// Convert from an arbitrary `PyObject` or panic.
        ///
        /// # Safety
        ///
        /// Relies on [`from_owned_ptr_or_opt`](#method.from_owned_ptr_or_opt).
        unsafe fn from_owned_ptr(py: Python<'p>, ptr: *mut ffi::PyObject) -> &'p Self {
            Self::from_owned_ptr_or_panic(py, ptr)
        }
        /// Convert from an arbitrary `PyObject`.
        ///
        /// # Safety
        ///
        /// Relies on [`from_owned_ptr_or_opt`](#method.from_owned_ptr_or_opt).
        unsafe fn from_owned_ptr_or_err(py: Python<'p>, ptr: *mut ffi::PyObject) -> PyResult<&'p Self> {
            Self::from_owned_ptr_or_opt(py, ptr).ok_or_else(|| err::PyErr::fetch(py))
        }
        /// Convert from an arbitrary borrowed `PyObject`.
        ///
        /// # Safety
        ///
        /// Implementations must ensure the object does not get freed during `'p` and avoid type confusion.
        unsafe fn from_borrowed_ptr_or_opt(py: Python<'p>, ptr: *mut ffi::PyObject)
            -> Option<&'p Self>;
        /// Convert from an arbitrary borrowed `PyObject`.
        ///
        /// # Safety
        ///
        /// Relies on unsafe fn [`from_borrowed_ptr_or_opt`](#method.from_borrowed_ptr_or_opt).
        unsafe fn from_borrowed_ptr_or_panic(py: Python<'p>, ptr: *mut ffi::PyObject) -> &'p Self {
            Self::from_borrowed_ptr_or_opt(py, ptr).unwrap_or_else(|| err::panic_after_error(py))
        }
        /// Convert from an arbitrary borrowed `PyObject`.
        ///
        /// # Safety
        ///
        /// Relies on unsafe fn [`from_borrowed_ptr_or_opt`](#method.from_borrowed_ptr_or_opt).
        unsafe fn from_borrowed_ptr(py: Python<'p>, ptr: *mut ffi::PyObject) -> &'p Self {
            Self::from_borrowed_ptr_or_panic(py, ptr)
        }
        /// Convert from an arbitrary borrowed `PyObject`.
        ///
        /// # Safety
        ///
        /// Relies on unsafe fn [`from_borrowed_ptr_or_opt`](#method.from_borrowed_ptr_or_opt).
        unsafe fn from_borrowed_ptr_or_err(
            py: Python<'p>,
            ptr: *mut ffi::PyObject,
        ) -> PyResult<&'p Self> {
            Self::from_borrowed_ptr_or_opt(py, ptr).ok_or_else(|| err::PyErr::fetch(py))
        }
    }

    unsafe impl<'p, T> FromPyPointer<'p> for T
    where
        T: 'p + crate::PyNativeType,
    {
        unsafe fn from_owned_ptr_or_opt(py: Python<'p>, ptr: *mut ffi::PyObject) -> Option<&'p Self> {
            gil::register_owned(py, NonNull::new(ptr)?);
            Some(&*(ptr as *mut Self))
        }
        unsafe fn from_borrowed_ptr_or_opt(
            _py: Python<'p>,
            ptr: *mut ffi::PyObject,
        ) -> Option<&'p Self> {
            NonNull::new(ptr as *mut Self).map(|p| &*p.as_ptr())
        }
    }

    #[cfg(test)]
    mod test {
        use crate::types::{IntoPyDict, PyAny, PyDict, PyList};
        use crate::{Python, ToPyObject};

        use super::PyTryFrom;

        #[test]
        fn test_try_from() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let list: &PyAny = vec![3, 6, 5, 4, 7].to_object(py).into_ref(py);
            let dict: &PyAny = vec![("reverse", true)].into_py_dict(py).as_ref();

            assert!(PyList::try_from(list).is_ok());
            assert!(PyDict::try_from(dict).is_ok());

            assert!(PyAny::try_from(list).is_ok());
            assert!(PyAny::try_from(dict).is_ok());
        }

        #[test]
        fn test_try_from_exact() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let list: &PyAny = vec![3, 6, 5, 4, 7].to_object(py).into_ref(py);
            let dict: &PyAny = vec![("reverse", true)].into_py_dict(py).as_ref();

            assert!(PyList::try_from_exact(list).is_ok());
            assert!(PyDict::try_from_exact(dict).is_ok());

            assert!(PyAny::try_from_exact(list).is_err());
            assert!(PyAny::try_from_exact(dict).is_err());
        }

        #[test]
        fn test_try_from_unchecked() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let list = PyList::new(py, &[1, 2, 3]);
            let val = unsafe { <PyList as PyTryFrom>::try_from_unchecked(list.as_ref()) };
            assert_eq!(list, val);
        }
    }