pythonrandomprobabilitycoin-flipping

How do I simulate flip of biased coin?


In unbiased coin flip H or T occurs 50% of times.

But I want to simulate coin which gives H with probability 'p' and T with probability '(1-p)'.

something like this:

def flip(p):
   '''this function return H with probability p'''
   # do something
   return result

>> [flip(0.8) for i in xrange(10)]
[H,H,T,H,H,H,T,H,H,H]

Solution

  • random.random() returns a uniformly distributed pseudo-random floating point number in the range [0, 1). This number is less than a given number p in the range [0,1) with probability p. Thus:

    def flip(p):
        return 'H' if random.random() < p else 'T'
    

    Some experiments:

    >>> N = 100
    >>> flips = [flip(0.2) for i in xrange(N)]
    >>> float(flips.count('H'))/N
    0.17999999999999999  # Approximately 20% of the coins are heads
    
    >>> N = 10000
    >>> flips = [flip(0.2) for i in xrange(N)]
    >>> float(flips.count('H'))/N
    0.20549999999999999  # Better approximation