pyo3/types/

sequence.rs

use crate::err::{self, PyErr, PyResult};
use crate::ffi_ptr_ext::FfiPtrExt;
#[cfg(feature = "experimental-inspect")]
use crate::inspect::{type_hint_identifier, PyStaticExpr};
use crate::instance::Bound;
use crate::internal_tricks::get_ssize_index;
use crate::py_result_ext::PyResultExt;
use crate::sync::PyOnceLock;
use crate::type_object::PyTypeInfo;
use crate::types::{any::PyAnyMethods, PyAny, PyList, PyTuple, PyType, PyTypeMethods};
use crate::{ffi, Borrowed, BoundObject, IntoPyObject, IntoPyObjectExt, Py, Python};

/// Represents a reference to a Python object supporting the sequence protocol.
///
/// Values of this type are accessed via PyO3's smart pointers, e.g. as
/// [`Py<PySequence>`][crate::Py] or [`Bound<'py, PySequence>`][Bound].
///
/// For APIs available on sequence objects, see the [`PySequenceMethods`] trait which is implemented for
/// [`Bound<'py, PySequence>`][Bound].
#[repr(transparent)]
pub struct PySequence(PyAny);

pyobject_native_type_named!(PySequence);

unsafe impl PyTypeInfo for PySequence {
    const NAME: &'static str = "Sequence";
    const MODULE: Option<&'static str> = Some("collections.abc");

    #[cfg(feature = "experimental-inspect")]
    const TYPE_HINT: PyStaticExpr = type_hint_identifier!("collections.abc", "Sequence");

    #[inline]
    fn type_object_raw(py: Python<'_>) -> *mut ffi::PyTypeObject {
        static TYPE: PyOnceLock<Py<PyType>> = PyOnceLock::new();
        TYPE.import(py, "collections.abc", "Sequence")
            .unwrap()
            .as_type_ptr()
    }

    #[inline]
    fn is_type_of(object: &Bound<'_, PyAny>) -> bool {
        // Using `is_instance` for `collections.abc.Sequence` is slow, so provide
        // optimized cases for list and tuples as common well-known sequences
        PyList::is_type_of(object)
            || PyTuple::is_type_of(object)
            || object
                .is_instance(&Self::type_object(object.py()).into_any())
                .unwrap_or_else(|err| {
                    err.write_unraisable(object.py(), Some(object));
                    false
                })
    }
}

impl PySequence {
    /// Register a pyclass as a subclass of `collections.abc.Sequence` (from the Python standard
    /// library). This is equivalent to `collections.abc.Sequence.register(T)` in Python.
    /// This registration is required for a pyclass to be castable from `PyAny` to `PySequence`.
    pub fn register<T: PyTypeInfo>(py: Python<'_>) -> PyResult<()> {
        let ty = T::type_object(py);
        Self::type_object(py).call_method1("register", (ty,))?;
        Ok(())
    }
}

/// Implementation of functionality for [`PySequence`].
///
/// These methods are defined for the `Bound<'py, PySequence>` smart pointer, so to use method call
/// syntax these methods are separated into a trait, because stable Rust does not yet support
/// `arbitrary_self_types`.
#[doc(alias = "PySequence")]
pub trait PySequenceMethods<'py>: crate::sealed::Sealed {
    /// Returns the number of objects in sequence.
    ///
    /// This is equivalent to the Python expression `len(self)`.
    fn len(&self) -> PyResult<usize>;

    /// Returns whether the sequence is empty.
    fn is_empty(&self) -> PyResult<bool>;

    /// Returns the concatenation of `self` and `other`.
    ///
    /// This is equivalent to the Python expression `self + other`.
    fn concat(&self, other: &Bound<'_, PySequence>) -> PyResult<Bound<'py, PySequence>>;

    /// Returns the result of repeating a sequence object `count` times.
    ///
    /// This is equivalent to the Python expression `self * count`.
    fn repeat(&self, count: usize) -> PyResult<Bound<'py, PySequence>>;

    /// Concatenates `self` and `other`, in place if possible.
    ///
    /// This is equivalent to the Python expression `self.__iadd__(other)`.
    ///
    /// The Python statement `self += other` is syntactic sugar for `self =
    /// self.__iadd__(other)`.  `__iadd__` should modify and return `self` if
    /// possible, but create and return a new object if not.
    fn in_place_concat(&self, other: &Bound<'_, PySequence>) -> PyResult<Bound<'py, PySequence>>;

    /// Repeats the sequence object `count` times and updates `self`, if possible.
    ///
    /// This is equivalent to the Python expression `self.__imul__(other)`.
    ///
    /// The Python statement `self *= other` is syntactic sugar for `self =
    /// self.__imul__(other)`.  `__imul__` should modify and return `self` if
    /// possible, but create and return a new object if not.
    fn in_place_repeat(&self, count: usize) -> PyResult<Bound<'py, PySequence>>;

    /// Returns the `index`th element of the Sequence.
    ///
    /// This is equivalent to the Python expression `self[index]` without support of negative indices.
    fn get_item(&self, index: usize) -> PyResult<Bound<'py, PyAny>>;

    /// Returns the slice of sequence object between `begin` and `end`.
    ///
    /// This is equivalent to the Python expression `self[begin:end]`.
    fn get_slice(&self, begin: usize, end: usize) -> PyResult<Bound<'py, PySequence>>;

    /// Assigns object `item` to the `i`th element of self.
    ///
    /// This is equivalent to the Python statement `self[i] = v`.
    fn set_item<I>(&self, i: usize, item: I) -> PyResult<()>
    where
        I: IntoPyObject<'py>;

    /// Deletes the `i`th element of self.
    ///
    /// This is equivalent to the Python statement `del self[i]`.
    fn del_item(&self, i: usize) -> PyResult<()>;

    /// Assigns the sequence `v` to the slice of `self` from `i1` to `i2`.
    ///
    /// This is equivalent to the Python statement `self[i1:i2] = v`.
    fn set_slice(&self, i1: usize, i2: usize, v: &Bound<'_, PyAny>) -> PyResult<()>;

    /// Deletes the slice from `i1` to `i2` from `self`.
    ///
    /// This is equivalent to the Python statement `del self[i1:i2]`.
    fn del_slice(&self, i1: usize, i2: usize) -> PyResult<()>;

    /// Returns the number of occurrences of `value` in self, that is, return the
    /// number of keys for which `self[key] == value`.
    #[cfg(not(PyPy))]
    fn count<V>(&self, value: V) -> PyResult<usize>
    where
        V: IntoPyObject<'py>;

    /// Determines if self contains `value`.
    ///
    /// This is equivalent to the Python expression `value in self`.
    fn contains<V>(&self, value: V) -> PyResult<bool>
    where
        V: IntoPyObject<'py>;

    /// Returns the first index `i` for which `self[i] == value`.
    ///
    /// This is equivalent to the Python expression `self.index(value)`.
    fn index<V>(&self, value: V) -> PyResult<usize>
    where
        V: IntoPyObject<'py>;

    /// Returns a fresh list based on the Sequence.
    fn to_list(&self) -> PyResult<Bound<'py, PyList>>;

    /// Returns a fresh tuple based on the Sequence.
    fn to_tuple(&self) -> PyResult<Bound<'py, PyTuple>>;
}

impl<'py> PySequenceMethods<'py> for Bound<'py, PySequence> {
    #[inline]
    fn len(&self) -> PyResult<usize> {
        let v = unsafe { ffi::PySequence_Size(self.as_ptr()) };
        crate::err::error_on_minusone(self.py(), v)?;
        Ok(v as usize)
    }

    #[inline]
    fn is_empty(&self) -> PyResult<bool> {
        self.len().map(|l| l == 0)
    }

    #[inline]
    fn concat(&self, other: &Bound<'_, PySequence>) -> PyResult<Bound<'py, PySequence>> {
        unsafe {
            ffi::PySequence_Concat(self.as_ptr(), other.as_ptr())
                .assume_owned_or_err(self.py())
                .cast_into_unchecked()
        }
    }

    #[inline]
    fn repeat(&self, count: usize) -> PyResult<Bound<'py, PySequence>> {
        unsafe {
            ffi::PySequence_Repeat(self.as_ptr(), get_ssize_index(count))
                .assume_owned_or_err(self.py())
                .cast_into_unchecked()
        }
    }

    #[inline]
    fn in_place_concat(&self, other: &Bound<'_, PySequence>) -> PyResult<Bound<'py, PySequence>> {
        unsafe {
            ffi::PySequence_InPlaceConcat(self.as_ptr(), other.as_ptr())
                .assume_owned_or_err(self.py())
                .cast_into_unchecked()
        }
    }

    #[inline]
    fn in_place_repeat(&self, count: usize) -> PyResult<Bound<'py, PySequence>> {
        unsafe {
            ffi::PySequence_InPlaceRepeat(self.as_ptr(), get_ssize_index(count))
                .assume_owned_or_err(self.py())
                .cast_into_unchecked()
        }
    }

    #[inline]
    fn get_item(&self, index: usize) -> PyResult<Bound<'py, PyAny>> {
        unsafe {
            ffi::PySequence_GetItem(self.as_ptr(), get_ssize_index(index))
                .assume_owned_or_err(self.py())
        }
    }

    #[inline]
    fn get_slice(&self, begin: usize, end: usize) -> PyResult<Bound<'py, PySequence>> {
        unsafe {
            ffi::PySequence_GetSlice(self.as_ptr(), get_ssize_index(begin), get_ssize_index(end))
                .assume_owned_or_err(self.py())
                .cast_into_unchecked()
        }
    }

    #[inline]
    fn set_item<I>(&self, i: usize, item: I) -> PyResult<()>
    where
        I: IntoPyObject<'py>,
    {
        fn inner(
            seq: &Bound<'_, PySequence>,
            i: usize,
            item: Borrowed<'_, '_, PyAny>,
        ) -> PyResult<()> {
            err::error_on_minusone(seq.py(), unsafe {
                ffi::PySequence_SetItem(seq.as_ptr(), get_ssize_index(i), item.as_ptr())
            })
        }

        let py = self.py();
        inner(
            self,
            i,
            item.into_pyobject_or_pyerr(py)?.into_any().as_borrowed(),
        )
    }

    #[inline]
    fn del_item(&self, i: usize) -> PyResult<()> {
        err::error_on_minusone(self.py(), unsafe {
            ffi::PySequence_DelItem(self.as_ptr(), get_ssize_index(i))
        })
    }

    #[inline]
    fn set_slice(&self, i1: usize, i2: usize, v: &Bound<'_, PyAny>) -> PyResult<()> {
        err::error_on_minusone(self.py(), unsafe {
            ffi::PySequence_SetSlice(
                self.as_ptr(),
                get_ssize_index(i1),
                get_ssize_index(i2),
                v.as_ptr(),
            )
        })
    }

    #[inline]
    fn del_slice(&self, i1: usize, i2: usize) -> PyResult<()> {
        err::error_on_minusone(self.py(), unsafe {
            ffi::PySequence_DelSlice(self.as_ptr(), get_ssize_index(i1), get_ssize_index(i2))
        })
    }

    #[inline]
    #[cfg(not(PyPy))]
    fn count<V>(&self, value: V) -> PyResult<usize>
    where
        V: IntoPyObject<'py>,
    {
        fn inner(seq: &Bound<'_, PySequence>, value: Borrowed<'_, '_, PyAny>) -> PyResult<usize> {
            let r = unsafe { ffi::PySequence_Count(seq.as_ptr(), value.as_ptr()) };
            crate::err::error_on_minusone(seq.py(), r)?;
            Ok(r as usize)
        }

        let py = self.py();
        inner(
            self,
            value.into_pyobject_or_pyerr(py)?.into_any().as_borrowed(),
        )
    }

    #[inline]
    fn contains<V>(&self, value: V) -> PyResult<bool>
    where
        V: IntoPyObject<'py>,
    {
        fn inner(seq: &Bound<'_, PySequence>, value: Borrowed<'_, '_, PyAny>) -> PyResult<bool> {
            let r = unsafe { ffi::PySequence_Contains(seq.as_ptr(), value.as_ptr()) };
            match r {
                0 => Ok(false),
                1 => Ok(true),
                _ => Err(PyErr::fetch(seq.py())),
            }
        }

        let py = self.py();
        inner(
            self,
            value.into_pyobject_or_pyerr(py)?.into_any().as_borrowed(),
        )
    }

    #[inline]
    fn index<V>(&self, value: V) -> PyResult<usize>
    where
        V: IntoPyObject<'py>,
    {
        fn inner(seq: &Bound<'_, PySequence>, value: Borrowed<'_, '_, PyAny>) -> PyResult<usize> {
            let r = unsafe { ffi::PySequence_Index(seq.as_ptr(), value.as_ptr()) };
            crate::err::error_on_minusone(seq.py(), r)?;
            Ok(r as usize)
        }

        let py = self.py();
        inner(
            self,
            value.into_pyobject_or_pyerr(py)?.into_any().as_borrowed(),
        )
    }

    #[inline]
    fn to_list(&self) -> PyResult<Bound<'py, PyList>> {
        unsafe {
            ffi::PySequence_List(self.as_ptr())
                .assume_owned_or_err(self.py())
                .cast_into_unchecked()
        }
    }

    #[inline]
    fn to_tuple(&self) -> PyResult<Bound<'py, PyTuple>> {
        unsafe {
            ffi::PySequence_Tuple(self.as_ptr())
                .assume_owned_or_err(self.py())
                .cast_into_unchecked()
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::platform::prelude::*;
    use crate::types::{PyAnyMethods, PyList, PySequence, PySequenceMethods, PyTuple};
    use crate::{IntoPyObject, Py, PyAny, PyTypeInfo, Python};
    use core::ptr;

    fn get_object() -> Py<PyAny> {
        // Convenience function for getting a single unique object
        Python::attach(|py| {
            let obj = py.eval(c"object()", None, None).unwrap();

            obj.into_pyobject(py).unwrap().unbind()
        })
    }

    #[test]
    fn test_numbers_are_not_sequences() {
        Python::attach(|py| {
            let v = 42i32;
            assert!(v.into_pyobject(py).unwrap().cast::<PySequence>().is_err());
        });
    }

    #[test]
    fn test_strings_are_sequences() {
        Python::attach(|py| {
            let v = "London Calling";
            assert!(v.into_pyobject(py).unwrap().cast::<PySequence>().is_ok());
        });
    }

    #[test]
    fn test_seq_empty() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert_eq!(0, seq.len().unwrap());

            let needle = 7i32.into_pyobject(py).unwrap();
            assert!(!seq.contains(&needle).unwrap());
        });
    }

    #[test]
    fn test_seq_is_empty() {
        Python::attach(|py| {
            let list = vec![1].into_pyobject(py).unwrap();
            let seq = list.cast::<PySequence>().unwrap();
            assert!(!seq.is_empty().unwrap());
            let vec: Vec<u32> = Vec::new();
            let empty_list = vec.into_pyobject(py).unwrap();
            let empty_seq = empty_list.cast::<PySequence>().unwrap();
            assert!(empty_seq.is_empty().unwrap());
        });
    }

    #[test]
    fn test_seq_contains() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert_eq!(6, seq.len().unwrap());

            let bad_needle = 7i32.into_pyobject(py).unwrap();
            assert!(!seq.contains(&bad_needle).unwrap());

            let good_needle = 8i32.into_pyobject(py).unwrap();
            assert!(seq.contains(&good_needle).unwrap());

            let type_coerced_needle = 8f32.into_pyobject(py).unwrap();
            assert!(seq.contains(&type_coerced_needle).unwrap());
        });
    }

    #[test]
    fn test_seq_get_item() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert_eq!(1, seq.get_item(0).unwrap().extract::<i32>().unwrap());
            assert_eq!(1, seq.get_item(1).unwrap().extract::<i32>().unwrap());
            assert_eq!(2, seq.get_item(2).unwrap().extract::<i32>().unwrap());
            assert_eq!(3, seq.get_item(3).unwrap().extract::<i32>().unwrap());
            assert_eq!(5, seq.get_item(4).unwrap().extract::<i32>().unwrap());
            assert_eq!(8, seq.get_item(5).unwrap().extract::<i32>().unwrap());
            assert!(seq.get_item(10).is_err());
        });
    }

    #[test]
    fn test_seq_del_item() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert!(seq.del_item(10).is_err());
            assert_eq!(1, seq.get_item(0).unwrap().extract::<i32>().unwrap());
            assert!(seq.del_item(0).is_ok());
            assert_eq!(1, seq.get_item(0).unwrap().extract::<i32>().unwrap());
            assert!(seq.del_item(0).is_ok());
            assert_eq!(2, seq.get_item(0).unwrap().extract::<i32>().unwrap());
            assert!(seq.del_item(0).is_ok());
            assert_eq!(3, seq.get_item(0).unwrap().extract::<i32>().unwrap());
            assert!(seq.del_item(0).is_ok());
            assert_eq!(5, seq.get_item(0).unwrap().extract::<i32>().unwrap());
            assert!(seq.del_item(0).is_ok());
            assert_eq!(8, seq.get_item(0).unwrap().extract::<i32>().unwrap());
            assert!(seq.del_item(0).is_ok());
            assert_eq!(0, seq.len().unwrap());
            assert!(seq.del_item(0).is_err());
        });
    }

    #[test]
    fn test_seq_set_item() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 2];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert_eq!(2, seq.get_item(1).unwrap().extract::<i32>().unwrap());
            assert!(seq.set_item(1, 10).is_ok());
            assert_eq!(10, seq.get_item(1).unwrap().extract::<i32>().unwrap());
        });
    }

    #[test]
    fn test_seq_set_item_refcnt() {
        let obj = get_object();

        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 2];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert!(seq.set_item(1, &obj).is_ok());
            assert!(ptr::eq(seq.get_item(1).unwrap().as_ptr(), obj.as_ptr()));
        });

        Python::attach(move |py| {
            assert_eq!(1, obj._get_refcnt(py));
        });
    }

    #[test]
    fn test_seq_get_slice() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert_eq!(
                [1, 2, 3],
                seq.get_slice(1, 4).unwrap().extract::<[i32; 3]>().unwrap()
            );
            assert_eq!(
                [3, 5, 8],
                seq.get_slice(3, 100)
                    .unwrap()
                    .extract::<[i32; 3]>()
                    .unwrap()
            );
        });
    }

    #[test]
    fn test_set_slice() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let w: Vec<i32> = vec![7, 4];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            let ins = w.into_pyobject(py).unwrap();
            seq.set_slice(1, 4, &ins).unwrap();
            assert_eq!([1, 7, 4, 5, 8], seq.extract::<[i32; 5]>().unwrap());
            seq.set_slice(3, 100, &PyList::empty(py)).unwrap();
            assert_eq!([1, 7, 4], seq.extract::<[i32; 3]>().unwrap());
        });
    }

    #[test]
    fn test_del_slice() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            seq.del_slice(1, 4).unwrap();
            assert_eq!([1, 5, 8], seq.extract::<[i32; 3]>().unwrap());
            seq.del_slice(1, 100).unwrap();
            assert_eq!([1], seq.extract::<[i32; 1]>().unwrap());
        });
    }

    #[test]
    fn test_seq_index() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert_eq!(0, seq.index(1i32).unwrap());
            assert_eq!(2, seq.index(2i32).unwrap());
            assert_eq!(3, seq.index(3i32).unwrap());
            assert_eq!(4, seq.index(5i32).unwrap());
            assert_eq!(5, seq.index(8i32).unwrap());
            assert!(seq.index(42i32).is_err());
        });
    }

    #[test]
    #[cfg(not(any(PyPy, GraalPy)))]
    fn test_seq_count() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert_eq!(2, seq.count(1i32).unwrap());
            assert_eq!(1, seq.count(2i32).unwrap());
            assert_eq!(1, seq.count(3i32).unwrap());
            assert_eq!(1, seq.count(5i32).unwrap());
            assert_eq!(1, seq.count(8i32).unwrap());
            assert_eq!(0, seq.count(42i32).unwrap());
        });
    }

    #[test]
    fn test_seq_iter() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 1, 2, 3, 5, 8];
            let ob = (&v).into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            let mut idx = 0;
            for el in seq.try_iter().unwrap() {
                assert_eq!(v[idx], el.unwrap().extract::<i32>().unwrap());
                idx += 1;
            }
            assert_eq!(idx, v.len());
        });
    }

    #[test]
    fn test_seq_strings() {
        Python::attach(|py| {
            let v = vec!["It", "was", "the", "worst", "of", "times"];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();

            let bad_needle = "blurst".into_pyobject(py).unwrap();
            assert!(!seq.contains(bad_needle).unwrap());

            let good_needle = "worst".into_pyobject(py).unwrap();
            assert!(seq.contains(good_needle).unwrap());
        });
    }

    #[test]
    fn test_seq_concat() {
        Python::attach(|py| {
            let v: Vec<i32> = vec![1, 2, 3];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            let concat_seq = seq.concat(seq).unwrap();
            assert_eq!(6, concat_seq.len().unwrap());
            let concat_v: Vec<i32> = vec![1, 2, 3, 1, 2, 3];
            for (el, cc) in concat_seq.try_iter().unwrap().zip(concat_v) {
                assert_eq!(cc, el.unwrap().extract::<i32>().unwrap());
            }
        });
    }

    #[test]
    fn test_seq_concat_string() {
        Python::attach(|py| {
            let v = "string";
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            let concat_seq = seq.concat(seq).unwrap();
            assert_eq!(12, concat_seq.len().unwrap());
            let concat_v = "stringstring".to_owned();
            for (el, cc) in seq.try_iter().unwrap().zip(concat_v.chars()) {
                assert_eq!(cc, el.unwrap().extract::<char>().unwrap());
            }
        });
    }

    #[test]
    fn test_seq_repeat() {
        Python::attach(|py| {
            let v = vec!["foo", "bar"];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            let repeat_seq = seq.repeat(3).unwrap();
            assert_eq!(6, repeat_seq.len().unwrap());
            let repeated = ["foo", "bar", "foo", "bar", "foo", "bar"];
            for (el, rpt) in repeat_seq.try_iter().unwrap().zip(repeated.iter()) {
                assert_eq!(*rpt, el.unwrap().extract::<String>().unwrap());
            }
        });
    }

    #[test]
    fn test_seq_inplace() {
        Python::attach(|py| {
            let v = vec!["foo", "bar"];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            let rep_seq = seq.in_place_repeat(3).unwrap();
            assert_eq!(6, seq.len().unwrap());
            assert!(seq.is(&rep_seq));

            let conc_seq = seq.in_place_concat(seq).unwrap();
            assert_eq!(12, seq.len().unwrap());
            assert!(seq.is(&conc_seq));
        });
    }

    #[test]
    fn test_list_coercion() {
        Python::attach(|py| {
            let v = vec!["foo", "bar"];
            let ob = (&v).into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert!(seq
                .to_list()
                .unwrap()
                .eq(PyList::new(py, &v).unwrap())
                .unwrap());
        });
    }

    #[test]
    fn test_strings_coerce_to_lists() {
        Python::attach(|py| {
            let v = "foo";
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert!(seq
                .to_list()
                .unwrap()
                .eq(PyList::new(py, ["f", "o", "o"]).unwrap())
                .unwrap());
        });
    }

    #[test]
    fn test_tuple_coercion() {
        Python::attach(|py| {
            let v = ("foo", "bar");
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert!(seq
                .to_tuple()
                .unwrap()
                .eq(PyTuple::new(py, ["foo", "bar"]).unwrap())
                .unwrap());
        });
    }

    #[test]
    fn test_lists_coerce_to_tuples() {
        Python::attach(|py| {
            let v = vec!["foo", "bar"];
            let ob = (&v).into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            assert!(seq
                .to_tuple()
                .unwrap()
                .eq(PyTuple::new(py, &v).unwrap())
                .unwrap());
        });
    }

    #[test]
    fn test_seq_cast_unchecked() {
        Python::attach(|py| {
            let v = vec!["foo", "bar"];
            let ob = v.into_pyobject(py).unwrap();
            let seq = ob.cast::<PySequence>().unwrap();
            let type_ptr = seq.as_any();
            let seq_from = unsafe { type_ptr.cast_unchecked::<PySequence>() };
            assert!(seq_from.to_list().is_ok());
        });
    }

    #[test]
    fn test_type_object() {
        Python::attach(|py| {
            let abc = PySequence::type_object(py);
            assert!(PyList::empty(py).is_instance(&abc).unwrap());
            assert!(PyTuple::empty(py).is_instance(&abc).unwrap());
        })
    }
}