Injective functions from N to X

inj_fun_n_x.py

>>> s="ABCD"
>>> repetition=3
>>> a = [i for i in itertools.permutations(s, repetition)]                                               
>>> len(a)  == math.factorial(len(s)) / math.factorial(len(s)-repetition)                          
True


def sample_function(n=0, s=set() ):
  f = {}
  for i in range(0, n):
    f[i]=random.choice(s)
    s.remove(f[i]) #injective functions here
  def _function(x):
    return f[x]
  return _function