Owerwrite regular conndions for correct working

Closed google#35434
Updated validations.py python script.
Fixed the behavior of validate_user function in validations.py.

Course3/Lab4/validations.py

@@ -13,12 +13,18 @@ def validate_user(username, minlen):
     if len(username) < minlen:
         return False
     # Usernames can only use letters, numbers, dots and underscores
-    if not re.match('^[a-z0-9._]*$', username):
+    if not re.match('[A-Za-z][\.a-zA-Z_]*$', username):
         return False
     # Usernames can't begin with a number
     if username[0].isnumeric():
         return False
     return True
 
+print(validate_user("blue.kale", 3)) # True
 
+print(validate_user(".blue.kale", 3)) # Currently True, should be False
+
+print(validate_user("red_quinoa", 4)) # True
+
+print(validate_user("_red_quinoa", 4)) # Currently True, should be False