Add size_hint() to PyIterator

vm/src/pyobject.rs

@@ -980,9 +980,12 @@ impl<T> PyIterable<T> {
             },
         )?;
 
+        let lenhint = objiter::length_hint(vm, iter_obj.clone())?;
+
         Ok(PyIterator {
             vm,
             obj: iter_obj,
+            lenhint,
             _item: std::marker::PhantomData,
         })
     }
@@ -991,6 +994,7 @@ impl<T> PyIterable<T> {
 pub struct PyIterator<'a, T> {
     vm: &'a VirtualMachine,
     obj: PyObjectRef,
+    lenhint: Option<usize>,
     _item: std::marker::PhantomData<T>,
 }
 
@@ -1012,6 +1016,10 @@ where
             }
         }
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.lenhint.unwrap_or(0), self.lenhint)
+    }
 }
 
 impl<T> TryFromObject for PyIterable<T>