I would do something like:

```python

# Regex for hex UUID format
hex_uuid_pattern = re.compile("^[0-F]{32}$", re.I)

# Validates that the given string is in hex UUID format
def is_valid_hex_uuid(val):
    return True if hex_uuid_pattern.match(value) is not None else False  

class KeystoneAwareClass:
      def push_tenant(self, tenant_id):
           # Keystone requires that the tenant ID is in hex UUID format
           if not is_valid_hex_uuid(self, tenant_id):
               warn("Probably bad format")
  ```
If you really insist that this method should be specific for keystone project ID check, then you can move 'is_valid_hex_uuid' inside the class but leave the pattern as generic.