[Python] OverflowError: long int too large to convert to float in python

I tried to calculate poisson distribution in python as below:

p = math.pow(3,idx)
depart = math.exp(-3) * p
depart = depart / math.factorial(idx)


idx ranges from 0

But I got OverflowError: long int too large to convert to float

I tried to convert depart to float but no results.

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