Transcript of the Towel demo video (towel 1.949).
The command took 3.4 seconds.

$ cat accounts.py
def register_user(form):
    user = dict(form)
    if not user.get("name"):
        raise ValueError("name is required")
    if len(user["name"]) < 2:
        raise ValueError("name is too short")
    return save(user)


def register_admin(form):
    admin = dict(form, role="admin")
    if not admin.get("name"):
        raise ValueError("name is required")
    if len(admin["name"]) < 8:
        raise ValueError("name is too short")
    return save(admin)

$ towel preview . --progress none
Would apply 1 refactoring(s).
Termination: fixed_point
--- before/accounts.py
+++ after/accounts.py
@@ -1,16 +1,16 @@
+def __extracted_func_0(__param_0, __param_1):
+    if not __param_0.get("name"):
+        raise ValueError("name is required")
+    if len(__param_0["name"]) < __param_1:
+        raise ValueError("name is too short")
+    return save(__param_0)
+
+
 def register_user(form):
     user = dict(form)
-    if not user.get("name"):
-        raise ValueError("name is required")
-    if len(user["name"]) < 2:
-        raise ValueError("name is too short")
-    return save(user)
+    return __extracted_func_0(user, 2)
 
 
 def register_admin(form):
     admin = dict(form, role="admin")
-    if not admin.get("name"):
-        raise ValueError("name is required")
-    if len(admin["name"]) < 8:
-        raise ValueError("name is too short")
-    return save(admin)
+    return __extracted_func_0(admin, 8)
Input files were not changed.