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Task/Benfords-law/Python/benfords-law.py

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+from __future__ import division
+from itertools import islice, count
+from collections import Counter
+from math import log10
+from random import randint
+
+expected = [log10(1+1/d) for d in range(1,10)]
+
+def fib():
+    a,b = 1,1
+    while True:
+        yield a
+        a,b = b,a+b
+
+# powers of 3 as a test sequence
+def power_of_threes():
+    return (3**k for k in count(0))
+
+def heads(s):
+    for a in s: yield int(str(a)[0])
+
+def show_dist(title, s):
+    c = Counter(s)
+    size = sum(c.values())
+    res = [c[d]/size for d in range(1,10)]
+
+    print("\n%s Benfords deviation" % title)
+    for r, e in zip(res, expected):
+        print("%5.1f%% %5.1f%%  %5.1f%%" % (r*100., e*100., abs(r - e)*100.))
+
+def rand1000():
+    while True: yield randint(1,9999)
+
+if __name__ == '__main__':
+    show_dist("fibbed", islice(heads(fib()), 1000))
+    show_dist("threes", islice(heads(power_of_threes()), 1000))
+
+    # just to show that not all kind-of-random sets behave like that
+    show_dist("random", islice(heads(rand1000()), 10000))