Add PyList::slice and fix index types of PyList::insert and PyList::s…

…et_item.

NB: the behavior on out-of-range indices hasn't changed;
it was merely wrongly documented before.

See #1667

src/types/list.rs

@@ -83,9 +83,22 @@ impl PyList {
         }
     }
 
+    /// Takes a slice of the list from indices `low` to `high` and returns it as a new list.
+    ///
+    /// Out-of-range indices are clipped to `self.len()`.
+    pub fn slice(&self, low: usize, high: usize) -> &PyList {
+        unsafe {
+            self.py().from_owned_ptr(ffi::PyList_GetSlice(
+                self.as_ptr(),
+                low as isize,
+                high as isize,
+            ))
+        }
+    }
+
     /// Sets the item at the specified index.
     ///
-    /// Panics if the index is out of range.
+    /// Raises `IndexError` if the index is out of range.
     pub fn set_item<I>(&self, index: isize, item: I) -> PyResult<()>
     where
         I: ToPyObject,
@@ -110,13 +123,16 @@ impl PyList {
 
     /// Inserts an item at the specified index.
     ///
-    /// Panics if the index is out of range.
-    pub fn insert<I>(&self, index: isize, item: I) -> PyResult<()>
+    /// If `index >= self.len()`, inserts at the end.
+    pub fn insert<I>(&self, index: usize, item: I) -> PyResult<()>
     where
         I: ToBorrowedObject,
     {
         item.with_borrowed_ptr(self.py(), |item| unsafe {
-            err::error_on_minusone(self.py(), ffi::PyList_Insert(self.as_ptr(), index, item))
+            err::error_on_minusone(
+                self.py(),
+                ffi::PyList_Insert(self.as_ptr(), index as isize, item),
+            )
         })
     }
 
@@ -251,14 +267,27 @@ mod tests {
         });
     }
 
+    #[test]
+    fn test_slice() {
+        Python::with_gil(|py| {
+            let list = PyList::new(py, &[2, 3, 5, 7]);
+            let slice = list.slice(1, 3);
+            assert_eq!(2, slice.len());
+            let slice = list.slice(1, 7);
+            assert_eq!(3, slice.len());
+        });
+    }
+
     #[test]
     fn test_set_item() {
         Python::with_gil(|py| {
             let list = PyList::new(py, &[2, 3, 5, 7]);
             let val = 42i32.to_object(py);
+            let val2 = 42i32.to_object(py);
             assert_eq!(2, list.get_item(0).extract::<i32>().unwrap());
             list.set_item(0, val).unwrap();
             assert_eq!(42, list.get_item(0).extract::<i32>().unwrap());
+            assert!(list.set_item(10, val2).is_err());
         });
     }
 
@@ -285,12 +314,15 @@ mod tests {
         Python::with_gil(|py| {
             let list = PyList::new(py, &[2, 3, 5, 7]);
             let val = 42i32.to_object(py);
+            let val2 = 43i32.to_object(py);
             assert_eq!(4, list.len());
             assert_eq!(2, list.get_item(0).extract::<i32>().unwrap());
             list.insert(0, val).unwrap();
-            assert_eq!(5, list.len());
+            list.insert(1000, val2).unwrap();
+            assert_eq!(6, list.len());
             assert_eq!(42, list.get_item(0).extract::<i32>().unwrap());
             assert_eq!(2, list.get_item(1).extract::<i32>().unwrap());
+            assert_eq!(43, list.get_item(5).extract::<i32>().unwrap());
         });
     }