Python之禪 by Tim Peters
- 優(yōu)美勝于丑陋（Python以編寫優(yōu)美的代碼為目標(biāo)）
- 明了勝于晦澀（優(yōu)美的代碼應(yīng)當(dāng)是明了的练俐，命名規(guī)范，風(fēng)格相似）
- 簡潔勝于復(fù)雜（優(yōu)美的代碼應(yīng)當(dāng)是簡潔的驾锰，不要有復(fù)雜的內(nèi)部實現(xiàn)）
- 復(fù)雜勝于凌亂（如果復(fù)雜不可避免禾锤，那代碼間也不能有難懂的關(guān)系蛔屹，要保持接口簡潔）
- 扁平勝于嵌套（優(yōu)美的代碼應(yīng)當(dāng)是扁平的茂卦，不能有太多的嵌套）
- 間隔勝于緊湊（優(yōu)美的代碼有適當(dāng)?shù)拈g隔青团，不要奢望一行代碼解決問題）
- 可讀性很重要（優(yōu)美的代碼是可讀的）
- 即便假借特例的實用性之名譬巫，也不可違背這些規(guī)則（這些規(guī)則至高無上）
- 不要包容所有錯誤，除非您確定需要這樣做（精準(zhǔn)地捕獲異常督笆，不寫 except:pass 風(fēng)格的代碼）
- 當(dāng)存在多種可能芦昔，不要嘗試去猜測
- 而是盡量找一種，最好是唯一一種明顯的解決方案（如果不確定娃肿，就用窮舉法）
- 雖然這并不容易咕缎，因為您不是 Python 之父（這里的 Dutch 是指 Guido ）
- 做也許好過不做，但不假思索就動手還不如不做（動手之前要細(xì)思量）
- 如果您無法向人描述您的方案料扰，那肯定不是一個好方案凭豪；反之亦然（方案測評標(biāo)準(zhǔn)）
- 命名空間是一種絕妙的理念，我們應(yīng)當(dāng)多加利用（倡導(dǎo)與號召）
#!/usr/bin/env python
"""
=====================================
PEP 20 (The Zen of Python) by example
=====================================
Usage: %prog
:Author: Hunter Blanks, hblanks@artifex.org / hblanks@monetate.com
:Date: 2011-02-08 for PhillyPUG/philly.rb, revised 2011-02-10
Sources:
- http://artifex.org/~hblanks/talks/2011/pep20_by_example.pdf
- http://artifex.org/~hblanks/talks/2011/pep20_by_example.html
- http://artifex.org/~hblanks/talks/2011/pep20_by_example.py.txt
Dependencies for PDF output:
- Pygments 1.4
- pdflatex & the usual mess of latex packages
"""
from __future__ import with_statement
import sys
################################ preface ###############################
"""
"In his wisdom and in his Molisan poverty, Officer Ingravallo,
who seemed to live on silence... , in his wisdom, he sometimes
interrupted this silence and this sleep to enunciate some
theoretical idea (a general idea, that is) on the affairs of men,
and of women. At first sight, or rather, on first hearing, these
seemed banalities. They weren't banalities. And so, those rapid
declarations, which crackled on his lips like the sudden
illumination of a sulphur match, were revived in the ears of people
at a distance of hours, or of months, from their enunciation: as if
after a mysterious period of incubation. 'That's right!' the person
in question admitted, 'That's exactly what Ingravallo said to me.'"
- Carlo Emilio Gadda, *That Awful Mess on the Via Merulana*
"""
################################# text #################################
"""
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!
"""
################################### 1 ##################################
"""
Give me a function that takes a list of numbers and returns only the
even ones, divided by two.
"""
#-----------------------------------------------------------------------
halve_evens_only = lambda nums: map(lambda i: i/2, filter(lambda i: not i%2, nums))
#-----------------------------------------------------------------------
def halve_evens_only(nums):
return [i/2 for i in nums if not i % 2]
#-----------------------------------------------------------------------
print 'Beautiful is better than ugly.'
################################## 2 ###################################
"""
Load the cat, dog, and mouse models so we can edit instances of them.
"""
def load():
from menagerie.cat.models import *
from menagerie.dog.models import *
from menagerie.mouse.models import *
#-----------------------------------------------------------------------
def load():
from menagerie.models import cat as cat_models
from menagerie.models import dog as dog_models
from menagerie.models import mouse as mouse_models
#-----------------------------------------------------------------------
print 'Explicit is better than implicit.'
################################### 3 ##################################
"""
Can you write out these measurements to disk?
"""
measurements = [
{'weight': 392.3, 'color': 'purple', 'temperature': 33.4},
{'weight': 34.0, 'color': 'green', 'temperature': -3.1},
]
#-----------------------------------------------------------------------
def store(measurements):
import sqlalchemy
import sqlalchemy.types as sqltypes
db = sqlalchemy.create_engine('sqlite:///measurements.db')
db.echo = False
metadata = sqlalchemy.MetaData(db)
table = sqlalchemy.Table('measurements', metadata,
sqlalchemy.Column('id', sqltypes.Integer, primary_key=True),
sqlalchemy.Column('weight', sqltypes.Float),
sqlalchemy.Column('temperature', sqltypes.Float),
sqlalchemy.Column('color', sqltypes.String(32)),
)
table.create(checkfirst=True)
for measurement in measurements:
i = table.insert()
i.execute(**measurement)
#-----------------------------------------------------------------------
def store(measurements):
import json
with open('measurements.json', 'w') as f:
f.write(json.dumps(measurements))
#-----------------------------------------------------------------------
print 'Simple is better than complex.'
################################### 4 ##################################
"""
Can you write out those same measurements to a MySQL DB? I think we're
gonna have some measurements with multiple colors next week, by the way.
"""
#-----------------------------------------------------------------------
def store(measurements):
import sqlalchemy
import sqlalchemy.types as sqltypes
db = create_engine(
'mysql://user:password@localhost/db?charset=utf8&use_unicode=1')
db.echo = False
metadata = sqlalchemy.MetaData(db)
table = sqlalchemy.Table('measurements', metadata,
sqlalchemy.Column('id', sqltypes.Integer, primary_key=True),
sqlalchemy.Column('weight', sqltypes.Float),
sqlalchemy.Column('temperature', sqltypes.Float),
sqlalchemy.Column('color', sqltypes.String(32)),
)
table.create(checkfirst=True)
for measurement in measurements:
i = table.insert()
i.execute(**measurement)
#-----------------------------------------------------------------------
def store(measurements):
import MySQLdb
db = MySQLdb.connect(user='user', passwd="password", host='localhost', db="db")
c = db.cursor()
c.execute("""
CREATE TABLE IF NOT EXISTS measurements
id int(11) NOT NULL auto_increment,
weight float,
temperature float,
color varchar(32)
PRIMARY KEY id
ENGINE=InnoDB CHARSET=utf8
""")
insert_sql = (
"INSERT INTO measurements (weight, temperature, color) "
"VALUES (%s, %s, %s)")
for measurement in measurements:
c.execute(insert_sql,
(measurement['weight'], measurement['temperature'], measurement['color'])
)
#-----------------------------------------------------------------------
print 'Complex is better than complicated.'
################################### 5 ##################################
"""Identify this animal. """
#-----------------------------------------------------------------------
def identify(animal):
if animal.is_vertebrate():
noise = animal.poke()
if noise == 'moo':
return 'cow'
elif noise == 'woof':
return 'dog'
else:
if animal.is_multicellular():
return 'Bug!'
else:
if animal.is_fungus():
return 'Yeast'
else:
return 'Amoeba'
#-----------------------------------------------------------------------
def identify(animal):
if animal.is_vertebrate():
return identify_vertebrate()
else:
return identify_invertebrate()
def identify_vertebrate(animal):
noise = animal.poke()
if noise == 'moo':
return 'cow'
elif noise == 'woof':
return 'dog'
def identify_invertebrate(animal):
if animal.is_multicellular():
return 'Bug!'
else:
if animal.is_fungus():
return 'Yeast'
else:
return 'Amoeba'
#-----------------------------------------------------------------------
print 'Flat is better than nested.'
################################### 6 ##################################
""" Parse an HTTP response object, yielding back new requests or data. """
#-----------------------------------------------------------------------
def process(response):
selector = lxml.cssselect.CSSSelector('#main > div.text')
lx = lxml.html.fromstring(response.body)
title = lx.find('./head/title').text
links = [a.attrib['href'] for a in lx.find('./a') if 'href' in a.attrib]
for link in links:
yield Request(url=link)
divs = selector(lx)
if divs: yield Item(utils.lx_to_text(divs[0]))
#-----------------------------------------------------------------------
def process(response):
lx = lxml.html.fromstring(response.body)
title = lx.find('./head/title').text
links = [a.attrib['href'] for a in lx.find('./a') if 'href' in a.attrib]
for link in links:
yield Request(url=link)
selector = lxml.cssselect.CSSSelector('#main > div.text')
divs = selector(lx)
if divs:
bodytext = utils.lx_to_text(divs[0])
yield Item(bodytext)
#-----------------------------------------------------------------------
print 'Sparse is better than dense.'
################################### 7 ##################################
""" Write out the tests for a factorial function. """
#-----------------------------------------------------------------------
def factorial(n):
"""
Return the factorial of n, an exact integer >= 0.
>>> [factorial(n) for n in range(6)]
[1, 1, 2, 6, 24, 120]
>>> factorial(30)
265252859812191058636308480000000L
>>> factorial(-1)
Traceback (most recent call last):
...
ValueError: n must be >= 0
"""
pass
if __name__ == '__main__' and '--test' in sys.argv:
import doctest
doctest.testmod()
#-----------------------------------------------------------------------
import unittest
def factorial(n):
pass
class FactorialTests(unittest.TestCase):
def test_ints(self):
self.assertEqual(
[factorial(n) for n in range(6)], [1, 1, 2, 6, 24, 120])
def test_long(self):
self.assertEqual(
factorial(30), 265252859812191058636308480000000L)
def test_negative_error(self):
with self.assertRaises(ValueError):
factorial(-1)
if __name__ == '__main__' and '--test' in sys.argv:
unittest.main()
#-----------------------------------------------------------------------
print 'Readability counts.'
################################# 8 & 9 ################################
"""
Write a function that returns another functions. Also, test floating point.
"""
#-----------------------------------------------------------------------
def make_counter():
i=0
def count():
""" Increments a count and returns it. """
i += 1
return i
return count
count = make_counter()
assert hasattr(count, '__name__') # No anonymous functions!
assert hasattr(count, '__doc__')
assert float('0.20000000000000007') == 1.1 - 0.9 # (this is platform dependent)
assert 0.2 != 1.1 - 0.9 # Not special enough to break the rules of floating pt.
assert float(repr(1.1 - 0.9)) == 1.1 - 0.9
#-----------------------------------------------------------------------
def make_adder(addend):
return lambda i: i + addend # But lambdas, once in a while, are practical.
assert str(1.1 - 0.9) == '0.2' # as may be rounding off floating point errors
assert round(0.2, 15) == round(1.1 - 0.9, 15)
#-----------------------------------------------------------------------
print "Special cases aren't special enough to break the rules."
print 'Although practicality beats purity.'
################################ 10 & 11 ###############################
""" Import whatever json library is available. """
try:
import json
except ImportError:
try:
import simplejson as json
except:
print 'Unable to find json module!'
raise
#-----------------------------------------------------------------------
print 'Errors should never pass silently'
print 'Unless explicitly silenced.'
################################## 12 ##################################
""" Store an HTTP request in the database. """
def process(response):
db.store(url, response.body)
#-----------------------------------------------------------------------
def process(response):
charset = detect_charset(response)
db.store(url, response.body.decode(charset))
print 'In the face of ambiguity, refuse the temptation to guess.'
################################## 13 ##################################
# Example 1
assert hasattr(__builtins__, 'map') # ('map' in __builtins__) raises TypeError
assert not hasattr(__builtins__, 'collect')
# Example 2
def fibonacci_generator():
prior, current = 0, 1
while current < 100:
yield prior + current
prior, current = current, current + prior
sequences = [
range(20),
{'foo': 1, 'fie': 2},
fibonacci_generator(),
(5, 3, 3)
]
for sequence in sequences:
for item in sequence: # all sequences iterate the same way
pass
#-----------------------------------------------------------------------
print 'There should be one, and preferably only one way to do it.'
print "Although that way may not be obvious at first unless you're Dutch."
################################## 14 ##################################
def obsolete_func():
raise PendingDeprecationWarning
def deprecated_func():
raise DeprecationWarning
print 'Now is better than never'
print 'Although never is often better than *right* now.'
################################## 15 ##################################
def hard():
# Example 1
try:
import twisted
help(twisted) # (this may not be as hard as I think, though)
except:
pass
# Example 2
import xml.dom.minidom
document = xml.dom.minidom.parseString(
'''<menagerie><cat>Fluffers</cat><cat>Cisco</cat></menagerie>''' )
menagerie = document.childNodes[0]
for node in menagerie.childNodes:
if node.childNodes[0].nodeValue== 'Cisco' and node.tagName == 'cat':
return node
def easy(maybe):
# Example 1
try:
import gevent
help(gevent)
except:
pass
# Example 2
import lxml
menagerie = lxml.etree.fromstring(
'''<menagerie><cat>Fluffers</cat><cat>Cisco</cat></menagerie>''' )
for pet in menagerie.find('./cat'):
if pet.text == 'Cisco':
return pet
print "If the implementation is hard to explain, it's a bad idea."
print 'If the implementation is easy to explain, it may be a good idea.'
################################## 16 ##################################
def chase():
import menagerie.models.cat as cat
import menagerie.models.dog as dog
dog.chase(cat)
cat.chase(mouse)
print "Namespaces are one honking great idea -- let's do more of those!"
############################### Readings ###############################
"""
- Peters, Tim. PEP 20, "The Zen of Python".
- Raymond, Eric. *The Art of Unix Programming*.
(http://www.catb.org/~esr/writings/taoup/)
- Alchin, Marty. *Pro Python*.
- Ramblings on
http://stackoverflow.com/questions/228181/the-zen-of-python
"""
############################## main block ##############################
from optparse import OptionParser
import os
import re
import subprocess
import sys
parser = OptionParser(usage=__doc__.strip())
parser.add_option('-v', dest='verbose', action='store_true',
help='Verbose output')
header_pat = re.compile(r'^\\PY\{c\}\{' + (r'\\PYZsh\{\}' * 8))
def yield_altered_lines(latex):
"""
Adds page breaks and page layout to our pygments file. Blah.
"""
for line in latex.splitlines():
if line == r'\documentclass{article}':
yield line
yield r'\usepackage{geometry}'
yield r'\geometry{letterpaper,landscape,margin=0.25in}'
elif line == r'\begin{document}':
yield line
yield r'\large'
elif header_pat.search(line):
yield r'\end{Verbatim}'
yield r'\pagebreak'
yield r'\begin{Verbatim}[commandchars=\\\{\}]'
yield line
else:
yield line
if __name__ == '__main__':
print
options, args = parser.parse_args()
if options.verbose:
errout = sys.stderr
else:
errout = open('/tmp/pep20.log', 'w')
try:
# TODO: pygmentize in Python instead of farming it out
p = subprocess.Popen(
('pygmentize', '-f', 'latex', '-l', 'python',
'-O', 'full', sys.argv[0]),
stdout=subprocess.PIPE, stderr=errout)
output, err = p.communicate()
assert p.returncode == 0, 'pygmentize exited with %d' % p.returncode
p2 = subprocess.Popen(
('pygmentize', '-f', 'html', '-l', 'python',
'-O', 'full', '-o', 'pep20_by_example.html', sys.argv[0]),
stdout=errout, stderr=errout)
p2.communicate()
assert p2.returncode == 0, 'pygmentize exited with %d' % p2.returncode
except OSError, e:
print >> sys.stderr, 'Failed to run pygmentize: %s' % str(e)
except AssertionError, e:
print e
altered_output = '\n'.join(l for l in yield_altered_lines(output))
try:
p = subprocess.Popen(('pdflatex',),
stdin=subprocess.PIPE, stdout=errout, stderr=errout)
p.communicate(altered_output)
assert p.returncode == 0, 'pdflatex exited with %d' % p.returncode
except OSError, e:
print >> sys.stderr, 'Failed to run pygmentize: %s' % str(e)
except AssertionError, e:
print e
os.rename('texput.pdf', 'pep20_by_example.pdf')
errout.close()
