Here is my implementation of a Pascal program, which is used to print an n-order Pascal triangle. This is actually an exercise I came up with to familiarize myself with Python's Functional Programming Modules.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import operator
from itertools import starmap, tee
from functools import lru_cache

def pairwise(iterable):
    s -> (s0,s1), (s1,s2), (s2,s3), ...
    a, b = tee(iterable)
    next(b, None)
    return zip(a, b)

def pascal_row(n):
    Print the nth row of a Pascal triangle
    if n < 2:
        return (x for x in [1])
        def dispatch():
            yield 1
            yield from starmap(operator.add, pairwise(pascal_row(n-1)))
            yield 1
        return dispatch()

def pascal(n):
    Print an n-order Pascal triangle
    for i in range(1, n):

print([x for x in pascal_row(500)])

Is this the right way of functional programming? Also, I want you to tell me how to make this piece of code clearer :)

  • 1
    \$\begingroup\$ I don't get how to use your pascal function. It just prints a bunch of generator expressions. Also, after the code has run, trying to call list(pascal_row(n)) with any n gives inconsistent behaviour. Try calling list(pascal_row(140)) followed by list(pascal_row(100)), followed by list(pascal_row(140)) again. The two results are completely different. Also, the list(pascal_row(100)) call returns [], which is obviously wrong. \$\endgroup\$ – Graipher Mar 21 '17 at 10:26
  • \$\begingroup\$ @Graipher Thanks for spotting so many errors for me! The inconsistency of pascal_row can be fixed by removing @lru_cache(), and I have to admit that my pascal function is wrong :( \$\endgroup\$ – nalzok Mar 21 '17 at 10:43

If you look at the documentation for lru_cache you'll see that it says that it can save time when an expensive or I/O bound function is periodically called with the same arguments. You keep calling pascal_row with different arguments and the cache will miss all the time. This can be seen if you put this at the end of your program the line:



CacheInfo(hits=0, misses=500, maxsize=128, currsize=128)

The only other thing I'd say is that you don't really need the -*- coding: utf-8 -*- line, UTF8 is the default and that's what you're using anyway.

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