How to combine initialization and assignment of dictionary in Python?
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I would like to figure out if any deal is selected twice or more.

The following example is stripped down for sake of readability. But in essence I thought the best solution would be using a dictionary, and whenever any deal-container (e.g. deal_pot_1) contains the same deal twice or more, I would capture it as an error.

The following code served me well, however by itself it throws an exception...
         

        if deal_pot_1:
           duplicates[deal_pot_1.pk] += 1

        if deal_pot_2:
            duplicates[deal_pot_2.pk] += 1

        if deal_pot_3:
            duplicates[deal_pot_3.pk] += 1

...if I didn't initialize this before hand like the following.


        if deal_pot_1:
           duplicates[deal_pot_1.pk] = 0

        if deal_pot_2:
            duplicates[deal_pot_2.pk] = 0

        if deal_pot_3:
            duplicates[deal_pot_3.pk] = 0

Is there anyway to simplify/combine this?