# Yet another Pascal triangle in Python written in functional programming pattern [closed]

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), ...
https://docs.python.org/3/library/itertools.html#itertools-recipes
"""
a, b = tee(iterable)
next(b, None)
return zip(a, b)

@lru_cache()
def pascal_row(n):
"""
Print the nth row of a Pascal triangle
"""
if n < 2:
return (x for x in [1])
else:
def dispatch():
yield 1
yield 1
return dispatch()

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

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 :)

• 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. – Graipher Mar 21 '17 at 10:26
• @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 :( – 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:
print(pascal_row.cache_info())
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.