Add __len__ to dictionary views.

Author: cthulahoops

tests/snippets/dict.py

@@ -68,6 +68,8 @@ def dict_eq(d1, d2):
 with assertRaises(TypeError):
     next(data.keys())
 
+assert len(data.keys()) == 2
+
 x = {}
 x[1] = 1
 assert x[1] == 1

vm/src/obj/objdict.rs

@@ -265,6 +265,11 @@ macro_rules! dict_iterator {
             fn iter(&self, _vm: &VirtualMachine) -> $iter_name {
                 $iter_name::new(self.dict.clone())
             }
+
+            #[pymethod(name = "__len__")]
+            fn len(&self, vm: &VirtualMachine) -> usize {
+                self.dict.clone().len(vm)
+            }
         }
 
         impl PyValue for $name {