$4.$ Message Class $($Derived from Activity$)$ Represents a user's message to another user. Inherits from the

Activity class.

Additional Attributes:

receiver $($User$)$: The user receiving the message.

Additional Methods:

Methods:

hw$2.$md $2024-01-26$

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$\_\_$str$\_\_($self$)$: Return a string representation of the Message.