Update src/makefun/main.py

Co-authored-by: Sylvain Marié <sylvain.marie@schneider-electric.com>

Author: andrewcleveland

src/makefun/main.py

@@ -15,6 +15,12 @@
 from textwrap import dedent
 from types import FunctionType
 
+
+if sys.version_info >= (3, 0):
+    is_identifier = str.isidentifier
+else:
+    from makefun._main_legacy_py import is_identifier
+
 try:  # python 3.3+
     from inspect import signature, Signature, Parameter
 except ImportError: