Thread Safety in Python's dictionary

I have a class which holds a dictionary

class OrderBook:
    orders = {'Restaurant1': None,
              'Restaurant2': None,
              'Restaurant3': None,
              'Restaurant4': None}

    @staticmethod
    def addOrder(restaurant_name, orders):
        OrderBook.orders[restaurant_name] = orders

And I am running 4 threads (one for each restaurant) that call the method OrderBook.addOrder. Here is the function ran by each thread:

def addOrders(restaurant_name):

    #creates orders
    ...

    OrderBook.addOrder(restaurant_name, orders)

Is this safe, or do I have to use a lock before calling addOrder?