Family Day update

Task/Sierpinski-triangle/Python/sierpinski-triangle-3.py

@@ -1,9 +1,12 @@
-from functools import (reduce)
-from operator import (add)
+'''Sierpinski triangle'''
+
+from functools import reduce
+from operator import add
 
 
 # sierpinski :: Int -> String
 def sierpinski(n):
+    '''Nth iteration of a Sierpinksi triangle.'''
     def go(xs, i):
         s = ' ' * (2 ** i)
         return concatMap(lambda x: [s + x + s])(xs) + (
@@ -14,6 +17,12 @@ def sierpinski(n):
 
 # concatMap :: (a -> [b]) -> [a] -> [b]
 def concatMap(f):
+    '''A concatenated list or string over which a function f
+       has been mapped.
+       The list monad can be derived by using an (a -> [b])
+       function which wraps its output in a list (using an
+       empty list to represent computational failure).
+    '''
     return lambda xs: (
         reduce(add, map(f, xs), [])
     )