diff --git a/cdd/__init__.py b/cdd/__init__.py
index 5c8f3253..611b6e74 100644
--- a/cdd/__init__.py
+++ b/cdd/__init__.py
@@ -8,7 +8,7 @@
 from logging import getLogger as get_logger
 
 __author__ = "Samuel Marks"
-__version__ = "0.0.99rc8"
+__version__ = "0.0.99rc9"
 __description__ = (
     "Open API to/fro routes, models, and tests. "
     "Convert between docstrings, classes, methods, argparse, pydantic, and SQLalchemy."
diff --git a/cdd/shared/pure_utils.py b/cdd/shared/pure_utils.py
index 12764aa2..7eec3150 100644
--- a/cdd/shared/pure_utils.py
+++ b/cdd/shared/pure_utils.py
@@ -2,6 +2,7 @@
 Pure utils for pure functions. For the same input will always produce the same input_str.
 """
 
+import string
 import typing
 from ast import Name, Str
 from collections import deque
@@ -1057,8 +1058,8 @@ def ensure_valid_identifier(s):
         return "{}_".format(s)
     elif s[0].isdigit():
         s = "_{}".format(s)
-    valid = frozenset("_ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")
-    return "".join(filter(valid.__contains__, s))
+    valid = frozenset("_{}{}".format(string.ascii_letters, string.digits))
+    return "".join(filter(valid.__contains__, s)) or "_"
 
 
 def set_attr(obj, key, val):
diff --git a/cdd/tests/test_shared/test_pure_utils.py b/cdd/tests/test_shared/test_pure_utils.py
index 2a4d4034..c4201a52 100644
--- a/cdd/tests/test_shared/test_pure_utils.py
+++ b/cdd/tests/test_shared/test_pure_utils.py
@@ -14,6 +14,7 @@
     blockwise,
     deindent,
     diff,
+    ensure_valid_identifier,
     find_module_filepath,
     get_module,
     identity,
@@ -69,6 +70,19 @@ def test_blockwise(self) -> None:
         self.assertTupleEqual(tuple(blockwise("ABC")), (("A", "B"), ("C", None)))
         self.assertTupleEqual(tuple(blockwise("ABCD")), (("A", "B"), ("C", "D")))
 
+    def test_ensure_valid_identifier(self) -> None:
+        """Tests that `ensure_valid_identifier` works"""
+        self.assertEqual(ensure_valid_identifier("_5"), "_5")
+        for ident in "foo", "bar", "can", "haz_", "_", "_5", "_a":
+            self.assertEqual(ensure_valid_identifier(ident), ident)
+        for ident in "6", "5":
+            self.assertEqual(ensure_valid_identifier(ident), "_{}".format(ident))
+        for ident in "for", "while", "break", "continue", "def", "class":
+            self.assertEqual(ensure_valid_identifier(ident), "{}_".format(ident))
+        for ident in "$", "-", "-%":
+            self.assertEqual(ensure_valid_identifier(ident), "_")
+        self.assertEqual(ensure_valid_identifier(""), "_")
+
     def test_find_module_filepath(self) -> None:
         """tests that it can `find_module_filepath`"""
         self.assertEqual(