mikebell.xyz


If you need a Computer Science tutor, code reviewer, or someone to pair program with, click here



The Zen of Python

description: This is from an older blog post at https://www.codementor.io/mikebell66/the-zen-of-python-s0cvequqn tags: python, python3, programming, PEP


Earlier tonight, a student of mine and I ran across a unique syntax:

def insertion_wrapper(f):
    # code goes here...


class LinkedList:
# some code for LinkedList class
# ...
    @_insertion_wrapper
    def insertion_sort(self):
        # code goes here...

And, in searching for help, I began reading from one of those PEPs

I forget which it was, no matter.

I was checking out the index and came across The Zen of Python.

I thought this was interesting.

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

Indeed, a beautiful post.

At the bottom of PEP 20 there is an “Easter Egg”…they tell us to import this

Doing so in a python3 terminal produces the above text.

Me being the enterprising, exploring hacker that I want to be, did the following:

$ python3
> import this
...
> this
<module 'this' from '/usr/lib/python3.6/this.py'>

INTERESTING!

Let us look at the contents of this file:

cat /usr/lib/python3.6/this.py                             
s = """Gur Mra bs Clguba, ol Gvz Crgref

Ornhgvshy vf orggre guna htyl.
Rkcyvpvg vf orggre guna vzcyvpvg.
Fvzcyr vf orggre guna pbzcyrk.
Pbzcyrk vf orggre guna pbzcyvpngrq.
Syng vf orggre guna arfgrq.
Fcnefr vf orggre guna qrafr.
Ernqnovyvgl pbhagf.
Fcrpvny pnfrf nera'g fcrpvny rabhtu gb oernx gur ehyrf.                                      
Nygubhtu cenpgvpnyvgl orngf chevgl.
Reebef fubhyq arire cnff fvyragyl.
Hayrff rkcyvpvgyl fvyraprq.
Va gur snpr bs nzovthvgl, ershfr gur grzcgngvba gb thrff.                                    
Gurer fubhyq or bar-- naq cersrenoyl bayl bar --boivbhf jnl gb qb vg.                        
Nygubhtu gung jnl znl abg or boivbhf ng svefg hayrff lbh'er Qhgpu.                           
Abj vf orggre guna arire.
Nygubhtu arire vf bsgra orggre guna *evtug* abj.                                             
Vs gur vzcyrzragngvba vf uneq gb rkcynva, vg'f n onq vqrn.                                   
Vs gur vzcyrzragngvba vf rnfl gb rkcynva, vg znl or n tbbq vqrn.                             
Anzrfcnprf ner bar ubaxvat terng vqrn -- yrg'f qb zber bs gubfr!"""                          

d = {}
for c in (65, 97):
    for i in range(26):
        d[chr(i+c)] = chr((i+13) % 26 + c)

print("".join([d.get(c, c) for c in s]))

So, there is some sort of basic cipher going on here.

Let us break it down…this is my first time looking at this:

for c in (65, 97):

65 is capital ‘A’ and 97 is lowercase ‘a’.

for i in range(26):

26 letters in the alphabet.

d[chr(i+c)] = chr((i+13) % 26 + c)

d is a dictionary.

The key into d is going to be chr(i+c). i is iterating from 0 to 26. Each entry into d is each alphabetic character in both upper and lowercase.

What about the value?

chr((i+13) % 26 + c)

Whoa, what’s going on here?

So, the letter i gets shifted up/forward/ahead by 13, then we mod that by 26 to give us yet another letter from A to Z, then we add the offset c.

d becomes a map on how to convert each character, effectively.

"".join([d.get(c,c) for c in s]))

It is snippets like this why I really love Python.

List comprehensions are great.

For each character c in s, we are grabbing the corresponding character from d.

It is a simple cipher, and kind of funny that this is built into Python.


If you need a Computer Science tutor, code reviewer, or just someone to pair program with, hit me up