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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 _next_unit_in_service(service, placed_in_services):
 """Return the unit number where to place a unit placed on a service. Receive the service name and a dict mapping service names to the current number of placed units in that service. """

    current = placed_in_services.get(service)
    number = 0 if current is None else current + 1
    placed_in_services[service] = number
    return number