#4748 lambda generators shouldn't return values

Lib/test/test_generators.py

@@ -928,6 +928,16 @@ Test the __name__ attribute and the repr()
 'f'
 >>> repr(g)  # doctest: +ELLIPSIS
 '<generator object f at ...>'
+
+Lambdas shouldn't have their usual return behavior.
+
+>>> x = lambda: (yield 1)
+>>> list(x())
+[1]
+
+>>> x = lambda: ((yield 1), (yield 2))
+>>> list(x())
+[1, 2]
 """
 
 # conjoin is a simple backtracking generator, named in honor of Icon's

Misc/NEWS

@@ -83,6 +83,8 @@ Core and Builtins
 - Issue #4509: Various issues surrounding resize of bytearray objects to
   which there are buffer exports.
 
+- Issue #4748: Lambda generators no longer return a value.
+
 Library
 -------
 

Python/compile.c

@@ -1534,7 +1534,12 @@ compiler_lambda(struct compiler *c, expr_ty e)
 	
 	c->u->u_argcount = asdl_seq_LEN(args->args);
 	VISIT_IN_SCOPE(c, expr, e->v.Lambda.body);
-	ADDOP_IN_SCOPE(c, RETURN_VALUE);
+	if (c->u->u_ste->ste_generator) {
+		ADDOP_IN_SCOPE(c, POP_TOP);
+	}
+	else {
+		ADDOP_IN_SCOPE(c, RETURN_VALUE);
+	}
 	co = assemble(c, 1);
 	compiler_exit_scope(c);
 	if (co == NULL)