当我们初写程序的时候,我们总会从一句最简单的话开始: hello world 当我们写python的时候,我们也有一段最基本的总纲——“this”. 打开python命令行,输入 import this 便会出现一段python之禅:

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The Zen of Python, by Tim Peters

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!

这是我们写python时应时时铭记的箴言。 那么就由这段富含哲理的开启我们的python源码之旅吧。 首先贴上this的源码:

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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])

一开头就是一个奇怪的字符串,不像是英文。如果有玩过凯撒密码的同学可能已经猜出来,这就是python之禅,不过经过了一点加密。 要看懂下面的几行代码,我们要知道chr函数是干嘛的。

chr.png 由图,chr是将数字转换成ascii表对应字符的函数,那么我们可以清楚地看出写出this的程序员的小把戏了: chr(65)是"A",chr(97)是"a",然后密文s的加密间距是13,即’A’对应’N',‘B’对应’O’,依次类推。 把所有的对应关系存到字典d中,最后再依靠列表推导式把s中对应字符一一存到一个列表中,再用join函数就打印出了我们最开始看到的python之禅。