per PR comment: move Python 2 is_identifier replacement from _main_legacy_py.py to main.py

Author: andrewcleveland

src/makefun/_main_legacy_py.py

@@ -88,14 +88,3 @@ def get_legacy_py_generator_body_template():
             # else:
             _y = _i.send(_s)     # let the implementation decide if None means "no new input" or "new input = None"
 """
-
-
-def is_identifier(string):
-    """
-    Replacement for `str.isidentifier` when it is not available (e.g. on Python 2).
-    :param string:
-    :return:
-    """
-    if len(string) == 0 or string[0].isdigit():
-        return False
-    return all([s.isalnum() for s in string.split("_")])

src/makefun/main.py

@@ -16,6 +16,19 @@
 from types import FunctionType
 
 
+if sys.version_info >= (3, 0):
+    is_identifier = str.isidentifier
+else:
+    def is_identifier(string):
+        """
+        Replacement for `str.isidentifier` when it is not available (e.g. on Python 2).
+        :param string:
+        :return:
+        """
+        if len(string) == 0 or string[0].isdigit():
+            return False
+        return all([s.isalnum() for s in string.split("_")])
+
 try:  # python 3.3+
     from inspect import signature, Signature, Parameter
 except ImportError:
@@ -1558,9 +1571,3 @@ def compile_fun_manually(target,
     new_f.__source__ = source_lines
 
     return new_f
-
-
-if sys.version_info >= (3, 0):
-    is_identifier = str.isidentifier
-else:
-    from makefun._main_legacy_py import is_identifier