Use format() instead of string interpolation, for old Python versions.

benchmarks/BUILD

@@ -84,11 +84,13 @@ py_binary(
 py_binary(
     name = "gen_upb_binary_c",
     srcs = ["gen_upb_binary_c.py"],
+    python_version = "PY3",
 )
 
 py_binary(
     name = "gen_protobuf_binary_cc",
     srcs = ["gen_protobuf_binary_cc.py"],
+    python_version = "PY3",
 )
 
 genrule(

benchmarks/gen_protobuf_binary_cc.py

@@ -11,22 +11,22 @@ if m:
   msg_basename = m.group(1)
   count = int(m.group(2))
 
-print(f'''
+print('''
 #include "{include}"
 
 char buf[1];
 
 int main() {{
-''')
+'''.format(include=include))
 
 def RefMessage(name):
-  print(f'''
+  print('''
   {{
     {name} proto;
     proto.ParseFromArray(buf, 0);
     proto.SerializePartialToArray(&buf[0], 0);
   }}
-  ''')
+  '''.format(name=name))
 
 RefMessage(msg_basename)
 

benchmarks/gen_upb_binary_c.py

@@ -11,7 +11,7 @@ if m:
   msg_basename = m.group(1)
   count = int(m.group(2))
 
-print(f'''
+print('''
 #include "{include}"
 
 char buf[1];
@@ -19,15 +19,15 @@ char buf[1];
 int main() {{
   upb_arena *arena = upb_arena_new();
   size_t size;
-''')
+'''.format(include=include))
 
 def RefMessage(name):
-  print(f'''
+  print('''
   {{
     {name} *proto = {name}_parse(buf, 1, arena);
     {name}_serialize(proto, arena, &size);
   }}
-  ''')
+  '''.format(name=name))
 
 RefMessage(msg_basename)