--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/python/example/factorial.py	Thu Sep 01 15:15:23 2016 -0700
@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+"""how many 0s are in a factorial"""
+
+import argparse
+import sys
+
+def factorial(N):
+    """factorial of `N`"""
+    if N == 1:
+        return 1
+    return reduce(int.__mul__, range(2, N+1))
+
+def factorial_zeros(N):
+    """how many 0s are in a factorial?"""
+
+    return N/5
+
+def main(args=sys.argv[1:]):
+    """CLI"""
+
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('N', type=int, nargs='+')
+    options = parser.parse_args(args)
+
+    # sanity
+    if any([i < 1 for i in options.N]):
+        parser.error("Input values must be >= 1")
+
+    for i in options.N:
+        f =  factorial(i)
+        print f
+
+if __name__ == '__main__':
+    main()