Add list.pop

Also include IndexError in the __builtin__ module.

tests/snippets/list.py

@@ -20,3 +20,11 @@ except ValueError:
     pass
 else:
     assert False, "ValueError was not raised"
+
+assert [1,2,'a'].pop() == 'a', "list pop failed"
+try:
+    [].pop()
+except IndexError:
+    pass
+else:
+    assert False, "IndexError was not raised"

vm/src/builtins.rs

@@ -822,6 +822,7 @@ pub fn make_module(ctx: &PyContext) -> PyObjectRef {
     );
     ctx.set_attr(&py_mod, "TypeError", ctx.exceptions.type_error.clone());
     ctx.set_attr(&py_mod, "ValueError", ctx.exceptions.value_error.clone());
+    ctx.set_attr(&py_mod, "IndexError", ctx.exceptions.index_error.clone());
 
     py_mod
 }

vm/src/obj/objlist.rs

@@ -272,6 +272,17 @@ fn list_mul(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(vm.ctx.new_list(new_elements))
 }
 
+fn list_pop(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
+    arg_check!(vm, args, required = [(zelf, Some(vm.ctx.list_type()))]);
+
+    let mut elements = get_mut_elements(zelf);
+    if let Some(result) = elements.pop() {
+        Ok(result)
+    } else {
+        Err(vm.new_index_error("pop from empty list".to_string()))
+    }
+}
+
 pub fn init(context: &PyContext) {
     let ref list_type = context.list_type;
     context.set_attr(&list_type, "__add__", context.new_rustfunc(list_add));
@@ -303,4 +314,5 @@ pub fn init(context: &PyContext) {
     context.set_attr(&list_type, "index", context.new_rustfunc(list_index));
     context.set_attr(&list_type, "reverse", context.new_rustfunc(list_reverse));
     context.set_attr(&list_type, "sort", context.new_rustfunc(list_sort));
+    context.set_attr(&list_type, "pop", context.new_rustfunc(list_pop));
 }