September Morn Update

Task/Long-multiplication/Python/long-multiplication-3.py

@@ -1,20 +1,43 @@
-#!/usr/bin/env python
+'''Long multiplication'''
 
-def digits(x):
-    return [int(c) for c in str(x)]
+from functools import reduce
 
-def mult_table(xs, ys):
-    return [[x * y for x in xs] for y in ys]
-
-def polymul(xs, ys):
-    return map(lambda *vs: sum(filter(None, vs)),
-               *[[0] * i + zs for i, zs in enumerate(mult_table(xs, ys))])
 
 def longmult(x, y):
-    result = 0
-    for v in polymul(digits(x), digits(y)):
-        result = result * 10 + v
-    return result
+    '''Long multiplication.'''
+    return reduce(
+        digitSum,
+        polymul(digits(x), digits(y)), 0
+    )
 
-if __name__ == "__main__":
-    print longmult(2**64, 2**64)
+
+def digitSum(a, x):
+    '''Left to right decimal digit summing.'''
+    return a * 10 + x
+
+
+def polymul(xs, ys):
+    '''List of specific products.'''
+    return map(
+        lambda *vs: sum(filter(None, vs)),
+        *[
+            [0] * i + zs for i, zs in
+            enumerate(mult_table(xs, ys))
+        ]
+    )
+
+
+def mult_table(xs, ys):
+    '''Rows of all products.'''
+    return [[x * y for x in xs] for y in ys]
+
+
+def digits(x):
+    '''Digits of x as a list of integers.'''
+    return [int(c) for c in str(x)]
+
+
+if __name__ == '__main__':
+    print(
+        longmult(2 ** 64, 2 ** 64)
+    )