OverflowError: long int too large to convert to float in python

Question

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)
         


        

Answer 1

The scipy module could help you.

scipy.misc.factorial is a factorial function that can use the gamma function approximation to calculate the factorial, and returns the result using floating points.

import numpy
from scipy.misc import factorial

i = numpy.arange(10)
print(numpy.exp(-3) * 3**i / factorial(i))

Gives:

[ 0.04978707  0.14936121  0.22404181  0.22404181  0.16803136  0.10081881
  0.05040941  0.02160403  0.00810151  0.0027005 ]

There is also a module to calculate Poisson distributions. For example:

import numpy
from scipy.stats import poisson

i = numpy.arange(10)
p = poisson(3)
print(p.pmf(i))

Gives:

[ 0.04978707  0.14936121  0.22404181  0.22404181  0.16803136  0.10081881
  0.05040941  0.02160403  0.00810151  0.0027005 ]