Further relax extract_sequence as neither PyObject::len nor PyObject:…

…:iter actually need the sequence protocol.

src/types/sequence.rs

@@ -299,18 +299,9 @@ fn extract_sequence<'s, T>(obj: &'s PyAny) -> PyResult<Vec<T>>
 where
  T: FromPyObject<'s>,
 {
- // Types that pass `PySequence_Check` usually implement enough of the sequence protocol
- // to support this function and if not, we will only fail extraction safely.
- let seq = unsafe {
- if ffi::PySequence_Check(obj.as_ptr()) != 0 {
- <PySequence as PyTryFrom>::try_from_unchecked(obj)
- } else {
- return Err(PyDowncastError::new(obj, "Sequence").into());
- }
- };
-
- let mut v = Vec::with_capacity(seq.len().unwrap_or(0) as usize);
- for item in seq.iter()? {
+ let iter = obj.iter()?;
+ let mut v = Vec::with_capacity(obj.len().unwrap_or(0) as usize);
+ for item in iter {
  v.push(item?.extract::<T>()?);
  }
  Ok(v)