# [Pyth](https://github.com/isaacg1/pyth), 8 bytes
    +\!s+R\!
[Try it online!](https://tio.run/##K6gsyfj/XztGsVg7KEbx/3@lxOIUhcS0rHxvhcRsq9SYvOyAIp@UmDwFIEjz9/J3tYawvd38Y/K83bJTC7LS8wsUitMLEvOzQGoSs5QA)

---
         Code | Explanation
    ----------+-------------------------------------
    +\!s+R\!  | Code
    +\!s+R\!Q | with implicit variables filled
    ----------+-------------------------------------
         R  Q | For each d in input, replace d with:
        +R\!  |  d+"!"
       s      | Join results on empty string
    +\!       | Add "!" to beginning
              | Print (implicit)