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

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    // Copyright (c) 2017 Daniel Grunwald
    //
    // Permission is hereby granted, free of charge, to any person obtaining a copy of this
    // software and associated documentation files (the "Software"), to deal in the Software
    // without restriction, including without limitation the rights to use, copy, modify, merge,
    // publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
    // to whom the Software is furnished to do so, subject to the following conditions:
    //
    // The above copyright notice and this permission notice shall be included in all copies or
    // substantial portions of the Software.
    //
    // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
    // INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
    // PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
    // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
    // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    // DEALINGS IN THE SOFTWARE.

    //! `PyBuffer` implementation
    use crate::err::{self, PyResult};
    use crate::{exceptions, ffi, AsPyPointer, FromPyObject, PyAny, PyNativeType, Python};
    use std::ffi::CStr;
    use std::marker::PhantomData;
    use std::os::raw;
    use std::pin::Pin;
    use std::{cell, mem, ptr, slice};

    /// Allows access to the underlying buffer used by a python object such as `bytes`, `bytearray` or `array.array`.
    // use Pin<Box> because Python expects that the Py_buffer struct has a stable memory address
    #[repr(transparent)]
    pub struct PyBuffer<T>(Pin<Box<ffi::Py_buffer>>, PhantomData<T>);

    // PyBuffer is thread-safe: the shape of the buffer is immutable while a Py_buffer exists.
    // Accessing the buffer contents is protected using the GIL.
    unsafe impl<T> Send for PyBuffer<T> {}
    unsafe impl<T> Sync for PyBuffer<T> {}

    #[derive(Copy, Clone, Eq, PartialEq)]
    pub enum ElementType {
        SignedInteger { bytes: usize },
        UnsignedInteger { bytes: usize },
        Bool,
        Float { bytes: usize },
        Unknown,
    }

    impl ElementType {
        pub fn from_format(format: &CStr) -> ElementType {
            match format.to_bytes() {
                [char] | [b'@', char] => native_element_type_from_type_char(*char),
                [modifier, char]
                    if (*modifier == b'='
                        || *modifier == b'<'
                        || *modifier == b'>'
                        || *modifier == b'!') =>
                {
                    standard_element_type_from_type_char(*char)
                }
                _ => ElementType::Unknown,
            }
        }
    }

    fn native_element_type_from_type_char(type_char: u8) -> ElementType {
        use self::ElementType::*;
        match type_char {
            b'c' => UnsignedInteger {
                bytes: mem::size_of::<raw::c_char>(),
            },
            b'b' => SignedInteger {
                bytes: mem::size_of::<raw::c_schar>(),
            },
            b'B' => UnsignedInteger {
                bytes: mem::size_of::<raw::c_uchar>(),
            },
            b'?' => Bool,
            b'h' => SignedInteger {
                bytes: mem::size_of::<raw::c_short>(),
            },
            b'H' => UnsignedInteger {
                bytes: mem::size_of::<raw::c_ushort>(),
            },
            b'i' => SignedInteger {
                bytes: mem::size_of::<raw::c_int>(),
            },
            b'I' => UnsignedInteger {
                bytes: mem::size_of::<raw::c_uint>(),
            },
            b'l' => SignedInteger {
                bytes: mem::size_of::<raw::c_long>(),
            },
            b'L' => UnsignedInteger {
                bytes: mem::size_of::<raw::c_ulong>(),
            },
            b'q' => SignedInteger {
                bytes: mem::size_of::<raw::c_longlong>(),
            },
            b'Q' => UnsignedInteger {
                bytes: mem::size_of::<raw::c_ulonglong>(),
            },
            b'n' => SignedInteger {
                bytes: mem::size_of::<libc::ssize_t>(),
            },
            b'N' => UnsignedInteger {
                bytes: mem::size_of::<libc::size_t>(),
            },
            b'e' => Float { bytes: 2 },
            b'f' => Float { bytes: 4 },
            b'd' => Float { bytes: 8 },
            _ => Unknown,
        }
    }

    fn standard_element_type_from_type_char(type_char: u8) -> ElementType {
        use self::ElementType::*;
        match type_char {
            b'c' | b'B' => UnsignedInteger { bytes: 1 },
            b'b' => SignedInteger { bytes: 1 },
            b'?' => Bool,
            b'h' => SignedInteger { bytes: 2 },
            b'H' => UnsignedInteger { bytes: 2 },
            b'i' | b'l' => SignedInteger { bytes: 4 },
            b'I' | b'L' => UnsignedInteger { bytes: 4 },
            b'q' => SignedInteger { bytes: 8 },
            b'Q' => UnsignedInteger { bytes: 8 },
            b'e' => Float { bytes: 2 },
            b'f' => Float { bytes: 4 },
            b'd' => Float { bytes: 8 },
            _ => Unknown,
        }
    }

    #[cfg(target_endian = "little")]
    fn is_matching_endian(c: u8) -> bool {
        c == b'@' || c == b'=' || c == b'>'
    }

    #[cfg(target_endian = "big")]
    fn is_matching_endian(c: u8) -> bool {
        c == b'@' || c == b'=' || c == b'>' || c == b'!'
    }

    /// Trait implemented for possible element types of `PyBuffer`.
    pub unsafe trait Element: Copy {
        /// Gets whether the element specified in the format string is potentially compatible.
        /// Alignment and size are checked separately from this function.
        fn is_compatible_format(format: &CStr) -> bool;
    }

    fn validate(b: &ffi::Py_buffer) -> PyResult<()> {
        // shape and stride information must be provided when we use PyBUF_FULL_RO
        if b.shape.is_null() {
            return Err(exceptions::PyBufferError::new_err("Shape is Null"));
        }
        if b.strides.is_null() {
            return Err(exceptions::PyBufferError::new_err(
                "PyBuffer: Strides is Null",
            ));
        }
        Ok(())
    }

    impl<'source, T: Element> FromPyObject<'source> for PyBuffer<T> {
        fn extract(obj: &PyAny) -> PyResult<PyBuffer<T>> {
            Self::get(obj)
        }
    }

    impl<T: Element> PyBuffer<T> {
        /// Get the underlying buffer from the specified python object.
        pub fn get(obj: &PyAny) -> PyResult<PyBuffer<T>> {
            unsafe {
                let mut buf = Box::pin(ffi::Py_buffer::new());
                err::error_on_minusone(
                    obj.py(),
                    ffi::PyObject_GetBuffer(obj.as_ptr(), &mut *buf, ffi::PyBUF_FULL_RO),
                )?;
                validate(&buf)?;
                let buf = PyBuffer(buf, PhantomData);
                // Type Check
                if mem::size_of::<T>() == buf.item_size()
                    && (buf.0.buf as usize) % mem::align_of::<T>() == 0
                    && T::is_compatible_format(buf.format())
                {
                    Ok(buf)
                } else {
                    Err(exceptions::PyBufferError::new_err(
                        "Incompatible type as buffer",
                    ))
                }
            }
        }

        /// Gets the pointer to the start of the buffer memory.
        ///
        /// Warning: the buffer memory might be mutated by other Python functions,
        /// and thus may only be accessed while the GIL is held.
        #[inline]
        pub fn buf_ptr(&self) -> *mut raw::c_void {
            self.0.buf
        }

        /// Gets a pointer to the specified item.
        ///
        /// If `indices.len() < self.dimensions()`, returns the start address of the sub-array at the specified dimension.
        pub fn get_ptr(&self, indices: &[usize]) -> *mut raw::c_void {
            let shape = &self.shape()[..indices.len()];
            for i in 0..indices.len() {
                assert!(indices[i] < shape[i]);
            }
            unsafe {
                ffi::PyBuffer_GetPointer(
                    &*self.0 as *const ffi::Py_buffer as *mut ffi::Py_buffer,
                    indices.as_ptr() as *mut usize as *mut ffi::Py_ssize_t,
                )
            }
        }

        /// Gets whether the underlying buffer is read-only.
        #[inline]
        pub fn readonly(&self) -> bool {
            self.0.readonly != 0
        }

        /// Gets the size of a single element, in bytes.
        /// Important exception: when requesting an unformatted buffer, item_size still has the value
        #[inline]
        pub fn item_size(&self) -> usize {
            self.0.itemsize as usize
        }

        /// Gets the total number of items.
        #[inline]
        pub fn item_count(&self) -> usize {
            (self.0.len as usize) / (self.0.itemsize as usize)
        }

        /// `item_size() * item_count()`.
        /// For contiguous arrays, this is the length of the underlying memory block.
        /// For non-contiguous arrays, it is the length that the logical structure would have if it were copied to a contiguous representation.
        #[inline]
        pub fn len_bytes(&self) -> usize {
            self.0.len as usize
        }

        /// Gets the number of dimensions.
        ///
        /// May be 0 to indicate a single scalar value.
        #[inline]
        pub fn dimensions(&self) -> usize {
            self.0.ndim as usize
        }

        /// Returns an array of length `dimensions`. `shape()[i]` is the length of the array in dimension number `i`.
        ///
        /// May return None for single-dimensional arrays or scalar values (`dimensions() <= 1`);
        /// You can call `item_count()` to get the length of the single dimension.
        ///
        /// Despite Python using an array of signed integers, the values are guaranteed to be non-negative.
        /// However, dimensions of length 0 are possible and might need special attention.
        #[inline]
        pub fn shape(&self) -> &[usize] {
            unsafe { slice::from_raw_parts(self.0.shape as *const usize, self.0.ndim as usize) }
        }

        /// Returns an array that holds, for each dimension, the number of bytes to skip to get to the next element in the dimension.
        ///
        /// Stride values can be any integer. For regular arrays, strides are usually positive,
        /// but a consumer MUST be able to handle the case `strides[n] <= 0`.
        #[inline]
        pub fn strides(&self) -> &[isize] {
            unsafe { slice::from_raw_parts(self.0.strides, self.0.ndim as usize) }
        }

        /// An array of length ndim.
        /// If `suboffsets[n] >= 0`, the values stored along the nth dimension are pointers and the suboffset value dictates how many bytes to add to each pointer after de-referencing.
        /// A suboffset value that is negative indicates that no de-referencing should occur (striding in a contiguous memory block).
        ///
        /// If all suboffsets are negative (i.e. no de-referencing is needed), then this field must be NULL (the default value).
        #[inline]
        pub fn suboffsets(&self) -> Option<&[isize]> {
            unsafe {
                if self.0.suboffsets.is_null() {
                    None
                } else {
                    Some(slice::from_raw_parts(
                        self.0.suboffsets,
                        self.0.ndim as usize,
                    ))
                }
            }
        }

        /// A NUL terminated string in struct module style syntax describing the contents of a single item.
        #[inline]
        pub fn format(&self) -> &CStr {
            if self.0.format.is_null() {
                CStr::from_bytes_with_nul(b"B\0").unwrap()
            } else {
                unsafe { CStr::from_ptr(self.0.format) }
            }
        }

        /// Gets whether the buffer is contiguous in C-style order (last index varies fastest when visiting items in order of memory address).
        #[inline]
        pub fn is_c_contiguous(&self) -> bool {
            unsafe {
                ffi::PyBuffer_IsContiguous(
                    &*self.0 as *const ffi::Py_buffer,
                    b'C' as std::os::raw::c_char,
                ) != 0
            }
        }

        /// Gets whether the buffer is contiguous in Fortran-style order (first index varies fastest when visiting items in order of memory address).
        #[inline]
        pub fn is_fortran_contiguous(&self) -> bool {
            unsafe {
                ffi::PyBuffer_IsContiguous(
                    &*self.0 as *const ffi::Py_buffer,
                    b'F' as std::os::raw::c_char,
                ) != 0
            }
        }

        /// Gets the buffer memory as a slice.
        ///
        /// This function succeeds if:
        /// * the buffer format is compatible with `T`
        /// * alignment and size of buffer elements is matching the expectations for type `T`
        /// * the buffer is C-style contiguous
        ///
        /// The returned slice uses type `Cell<T>` because it's theoretically possible for any call into the Python runtime
        /// to modify the values in the slice.
        pub fn as_slice<'a>(&'a self, _py: Python<'a>) -> Option<&'a [ReadOnlyCell<T>]> {
            if self.is_c_contiguous() {
                unsafe {
                    Some(slice::from_raw_parts(
                        self.0.buf as *mut ReadOnlyCell<T>,
                        self.item_count(),
                    ))
                }
            } else {
                None
            }
        }

        /// Gets the buffer memory as a slice.
        ///
        /// This function succeeds if:
        /// * the buffer is not read-only
        /// * the buffer format is compatible with `T`
        /// * alignment and size of buffer elements is matching the expectations for type `T`
        /// * the buffer is C-style contiguous
        ///
        /// The returned slice uses type `Cell<T>` because it's theoretically possible for any call into the Python runtime
        /// to modify the values in the slice.
        pub fn as_mut_slice<'a>(&'a self, _py: Python<'a>) -> Option<&'a [cell::Cell<T>]> {
            if !self.readonly() && self.is_c_contiguous() {
                unsafe {
                    Some(slice::from_raw_parts(
                        self.0.buf as *mut cell::Cell<T>,
                        self.item_count(),
                    ))
                }
            } else {
                None
            }
        }

        /// Gets the buffer memory as a slice.
        ///
        /// This function succeeds if:
        /// * the buffer format is compatible with `T`
        /// * alignment and size of buffer elements is matching the expectations for type `T`
        /// * the buffer is Fortran-style contiguous
        ///
        /// The returned slice uses type `Cell<T>` because it's theoretically possible for any call into the Python runtime
        /// to modify the values in the slice.
        pub fn as_fortran_slice<'a>(&'a self, _py: Python<'a>) -> Option<&'a [ReadOnlyCell<T>]> {
            if mem::size_of::<T>() == self.item_size() && self.is_fortran_contiguous() {
                unsafe {
                    Some(slice::from_raw_parts(
                        self.0.buf as *mut ReadOnlyCell<T>,
                        self.item_count(),
                    ))
                }
            } else {
                None
            }
        }

        /// Gets the buffer memory as a slice.
        ///
        /// This function succeeds if:
        /// * the buffer is not read-only
        /// * the buffer format is compatible with `T`
        /// * alignment and size of buffer elements is matching the expectations for type `T`
        /// * the buffer is Fortran-style contiguous
        ///
        /// The returned slice uses type `Cell<T>` because it's theoretically possible for any call into the Python runtime
        /// to modify the values in the slice.
        pub fn as_fortran_mut_slice<'a>(&'a self, _py: Python<'a>) -> Option<&'a [cell::Cell<T>]> {
            if !self.readonly() && self.is_fortran_contiguous() {
                unsafe {
                    Some(slice::from_raw_parts(
                        self.0.buf as *mut cell::Cell<T>,
                        self.item_count(),
                    ))
                }
            } else {
                None
            }
        }

        /// Copies the buffer elements to the specified slice.
        /// If the buffer is multi-dimensional, the elements are written in C-style order.
        ///
        ///  * Fails if the slice does not have the correct length (`buf.item_count()`).
        ///  * Fails if the buffer format is not compatible with type `T`.
        ///
        /// To check whether the buffer format is compatible before calling this method,
        /// you can use `<T as buffer::Element>::is_compatible_format(buf.format())`.
        /// Alternatively, `match buffer::ElementType::from_format(buf.format())`.
        pub fn copy_to_slice(&self, py: Python, target: &mut [T]) -> PyResult<()> {
            self.copy_to_slice_impl(py, target, b'C')
        }

        /// Copies the buffer elements to the specified slice.
        /// If the buffer is multi-dimensional, the elements are written in Fortran-style order.
        ///
        ///  * Fails if the slice does not have the correct length (`buf.item_count()`).
        ///  * Fails if the buffer format is not compatible with type `T`.
        ///
        /// To check whether the buffer format is compatible before calling this method,
        /// you can use `<T as buffer::Element>::is_compatible_format(buf.format())`.
        /// Alternatively, `match buffer::ElementType::from_format(buf.format())`.
        pub fn copy_to_fortran_slice(&self, py: Python, target: &mut [T]) -> PyResult<()> {
            self.copy_to_slice_impl(py, target, b'F')
        }

        fn copy_to_slice_impl(&self, py: Python, target: &mut [T], fort: u8) -> PyResult<()> {
            if mem::size_of_val(target) != self.len_bytes() {
                return Err(exceptions::PyBufferError::new_err(
                    "Slice length does not match buffer length.",
                ));
            }
            unsafe {
                err::error_on_minusone(
                    py,
                    ffi::PyBuffer_ToContiguous(
                        target.as_ptr() as *mut raw::c_void,
                        &*self.0 as *const ffi::Py_buffer as *mut ffi::Py_buffer,
                        self.0.len,
                        fort as std::os::raw::c_char,
                    ),
                )
            }
        }

        /// Copies the buffer elements to a newly allocated vector.
        /// If the buffer is multi-dimensional, the elements are written in C-style order.
        ///
        /// Fails if the buffer format is not compatible with type `T`.
        pub fn to_vec(&self, py: Python) -> PyResult<Vec<T>> {
            self.to_vec_impl(py, b'C')
        }

        /// Copies the buffer elements to a newly allocated vector.
        /// If the buffer is multi-dimensional, the elements are written in Fortran-style order.
        ///
        /// Fails if the buffer format is not compatible with type `T`.
        pub fn to_fortran_vec(&self, py: Python) -> PyResult<Vec<T>> {
            self.to_vec_impl(py, b'F')
        }

        fn to_vec_impl(&self, py: Python, fort: u8) -> PyResult<Vec<T>> {
            let item_count = self.item_count();
            let mut vec: Vec<T> = Vec::with_capacity(item_count);
            unsafe {
                // Copy the buffer into the uninitialized space in the vector.
                // Due to T:Copy, we don't need to be concerned with Drop impls.
                err::error_on_minusone(
                    py,
                    ffi::PyBuffer_ToContiguous(
                        vec.as_mut_ptr() as *mut raw::c_void,
                        &*self.0 as *const ffi::Py_buffer as *mut ffi::Py_buffer,
                        self.0.len,
                        fort as std::os::raw::c_char,
                    ),
                )?;
                // set vector length to mark the now-initialized space as usable
                vec.set_len(item_count);
            }
            Ok(vec)
        }

        /// Copies the specified slice into the buffer.
        /// If the buffer is multi-dimensional, the elements in the slice are expected to be in C-style order.
        ///
        ///  * Fails if the buffer is read-only.
        ///  * Fails if the slice does not have the correct length (`buf.item_count()`).
        ///  * Fails if the buffer format is not compatible with type `T`.
        ///
        /// To check whether the buffer format is compatible before calling this method,
        /// use `<T as buffer::Element>::is_compatible_format(buf.format())`.
        /// Alternatively, `match buffer::ElementType::from_format(buf.format())`.
        pub fn copy_from_slice(&self, py: Python, source: &[T]) -> PyResult<()> {
            self.copy_from_slice_impl(py, source, b'C')
        }

        /// Copies the specified slice into the buffer.
        /// If the buffer is multi-dimensional, the elements in the slice are expected to be in Fortran-style order.
        ///
        ///  * Fails if the buffer is read-only.
        ///  * Fails if the slice does not have the correct length (`buf.item_count()`).
        ///  * Fails if the buffer format is not compatible with type `T`.
        ///
        /// To check whether the buffer format is compatible before calling this method,
        /// use `<T as buffer::Element>::is_compatible_format(buf.format())`.
        /// Alternatively, `match buffer::ElementType::from_format(buf.format())`.
        pub fn copy_from_fortran_slice(&self, py: Python, source: &[T]) -> PyResult<()> {
            self.copy_from_slice_impl(py, source, b'F')
        }

        fn copy_from_slice_impl(&self, py: Python, source: &[T], fort: u8) -> PyResult<()> {
            if self.readonly() {
                return buffer_readonly_error();
            }
            if mem::size_of_val(source) != self.len_bytes() {
                return Err(exceptions::PyBufferError::new_err(
                    "Slice length does not match buffer length.",
                ));
            }
            unsafe {
                err::error_on_minusone(
                    py,
                    ffi::PyBuffer_FromContiguous(
                        &*self.0 as *const ffi::Py_buffer as *mut ffi::Py_buffer,
                        source.as_ptr() as *mut raw::c_void,
                        self.0.len,
                        fort as std::os::raw::c_char,
                    ),
                )
            }
        }

        pub fn release(self, _py: Python) {
            // First move self into a ManuallyDrop, so that PyBuffer::drop will
            // never be called. (It would acquire the GIL and call PyBuffer_Release
            // again.)
            let mut mdself = mem::ManuallyDrop::new(self);
            unsafe {
                // Next, make the actual PyBuffer_Release call.
                ffi::PyBuffer_Release(&mut *mdself.0);

                // Finally, drop the contained Pin<Box<_>> in place, to free the
                // Box memory.
                let inner: *mut Pin<Box<ffi::Py_buffer>> = &mut mdself.0;
                ptr::drop_in_place(inner);
            }
        }
    }

    #[inline(always)]
    fn buffer_readonly_error() -> PyResult<()> {
        Err(exceptions::PyBufferError::new_err(
            "Cannot write to read-only buffer.",
        ))
    }

    impl<T> Drop for PyBuffer<T> {
        fn drop(&mut self) {
            Python::with_gil(|_| unsafe { ffi::PyBuffer_Release(&mut *self.0) });
        }
    }

    /// Like `std::mem::cell`, but only provides read-only access to the data.
    ///
    /// `&ReadOnlyCell<T>` is basically a safe version of `*const T`:
    ///  The data cannot be modified through the reference, but other references may
    ///  be modifying the data.
    #[repr(transparent)]
    pub struct ReadOnlyCell<T: Element>(cell::UnsafeCell<T>);

    impl<T: Element> ReadOnlyCell<T> {
        #[inline]
        pub fn get(&self) -> T {
            unsafe { *self.0.get() }
        }

        #[inline]
        pub fn as_ptr(&self) -> *const T {
            self.0.get()
        }
    }

    macro_rules! impl_element(
        ($t:ty, $f:ident) => {
            unsafe impl Element for $t {
                fn is_compatible_format(format: &CStr) -> bool {
                    let slice = format.to_bytes();
                    if slice.len() > 1 && !is_matching_endian(slice[0]) {
                        return false;
                    }
                    ElementType::from_format(format) == ElementType::$f { bytes: mem::size_of::<$t>() }
                }
            }
        }
    );

    impl_element!(u8, UnsignedInteger);
    impl_element!(u16, UnsignedInteger);
    impl_element!(u32, UnsignedInteger);
    impl_element!(u64, UnsignedInteger);
    impl_element!(usize, UnsignedInteger);
    impl_element!(i8, SignedInteger);
    impl_element!(i16, SignedInteger);
    impl_element!(i32, SignedInteger);
    impl_element!(i64, SignedInteger);
    impl_element!(isize, SignedInteger);
    impl_element!(f32, Float);
    impl_element!(f64, Float);

    #[cfg(test)]
    mod test {
        use super::PyBuffer;
        use crate::ffi;
        use crate::Python;

        #[test]
        fn test_compatible_size() {
            // for the cast in PyBuffer::shape()
            assert_eq!(
                std::mem::size_of::<ffi::Py_ssize_t>(),
                std::mem::size_of::<usize>()
            );
        }

        #[test]
        fn test_bytes_buffer() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let bytes = py.eval("b'abcde'", None, None).unwrap();
            let buffer = PyBuffer::get(&bytes).unwrap();
            assert_eq!(buffer.dimensions(), 1);
            assert_eq!(buffer.item_count(), 5);
            assert_eq!(buffer.format().to_str().unwrap(), "B");
            assert_eq!(buffer.shape(), [5]);
            // single-dimensional buffer is always contiguous
            assert!(buffer.is_c_contiguous());
            assert!(buffer.is_fortran_contiguous());

            let slice = buffer.as_slice(py).unwrap();
            assert_eq!(slice.len(), 5);
            assert_eq!(slice[0].get(), b'a');
            assert_eq!(slice[2].get(), b'c');

            assert!(buffer.copy_to_slice(py, &mut [0u8]).is_err());
            let mut arr = [0; 5];
            buffer.copy_to_slice(py, &mut arr).unwrap();
            assert_eq!(arr, b"abcde" as &[u8]);

            assert!(buffer.copy_from_slice(py, &[0u8; 5]).is_err());
            assert_eq!(buffer.to_vec(py).unwrap(), b"abcde");
        }

        #[allow(clippy::float_cmp)] // The test wants to ensure that no precision was lost on the Python round-trip
        #[test]
        fn test_array_buffer() {
            let gil = Python::acquire_gil();
            let py = gil.python();
            let array = py
                .import("array")
                .unwrap()
                .call_method("array", ("f", (1.0, 1.5, 2.0, 2.5)), None)
                .unwrap();
            let buffer = PyBuffer::get(array).unwrap();
            assert_eq!(buffer.dimensions(), 1);
            assert_eq!(buffer.item_count(), 4);
            assert_eq!(buffer.format().to_str().unwrap(), "f");
            assert_eq!(buffer.shape(), [4]);

            let slice = buffer.as_slice(py).unwrap();
            assert_eq!(slice.len(), 4);
            assert_eq!(slice[0].get(), 1.0);
            assert_eq!(slice[3].get(), 2.5);

            let mut_slice = buffer.as_mut_slice(py).unwrap();
            assert_eq!(mut_slice.len(), 4);
            assert_eq!(mut_slice[0].get(), 1.0);
            mut_slice[3].set(2.75);
            assert_eq!(slice[3].get(), 2.75);

            buffer
                .copy_from_slice(py, &[10.0f32, 11.0, 12.0, 13.0])
                .unwrap();
            assert_eq!(slice[2].get(), 12.0);

            assert_eq!(buffer.to_vec(py).unwrap(), [10.0, 11.0, 12.0, 13.0]);
        }
    }