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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_user(self, username):
 """ Given the verified username, look up and return the corresponding user account if it exists, or raising ``ActivationError`` if it doesn't. """

        User = get_user_model()
        try:
            user = User.objects.get(**{
                User.USERNAME_FIELD: username,
            })
            if user.is_active:
                raise ActivationError(
                    self.ALREADY_ACTIVATED_MESSAGE,
                    code='already_activated'
                )
            return user
        except User.DoesNotExist:
            raise ActivationError(
                self.BAD_USERNAME_MESSAGE,
                code='bad_username'
            )