Python最佳编码实践

if ( (x==8) and (y>5) ) : ...

1<<5&2

return(5);

while (x<5) : ...

7.

if x == 8 and y > 5: ...

(1 << 5) & 2

return 5

while x < 5: ...

7.0

v[i + 1 + a] + v[i + 2 + b]

print x, x*x + 1

v[i+a+1] + v[i+b+2]

# 变量最好用描述性名称

# 小范围来说，短的变量名业务不错的选择。

dict = {‘alpha‘: 0x1234}

sum = x + y

values = [1, 2, 3]

symbol_address = {‘alpha‘: 0x1234}

tot = x + y

"""some string""" and ‘‘‘some string‘‘‘

# 上述的格式是一样，一样，一样的

if mapping.has_key(6): ...

if 6 in mapping: ...

def function(x, items=None): ...

if items is None:

items = []

if z > 5:

var1 = 55

# (或者总是用TAB键作为缩进，但这样同样不好)

x = 1

if z > 5:

var1 = 55

for key, val in mapping.items(): ...

for key in mapping.keys(): ...

mapping = {5: "5", 6: "6"}

for key, val in mapping.iteritems(): ...

for key in mapping: ...

# run when a module is executed and not

# imported:

if __name__ == ‘__main__‘:

python -m profile -o stats myscript.py

>>> import pstats

>>> p = pstats.Stats(‘stats‘)

>>> p.sort_stats(‘time‘).print_stats(15)

# -*- coding: UTF-8 -*-

# 或者如果你电脑内存不足，就干脆使用latin编码

# coding: latin

for i in xrange(len(al)-1, -1, -1):

del al[i]

del items[:]

# 如果程序速度不是最重要的话，可以仅仅新增加以个空列表：

items = []

# 如果你只想移除一个列表的引用值时，可以使用:

del items

xxx

until yyy

while True

xxx

if yyy: break

sys.path.append("some.zip")

b = 6

aux = a

a = b

b = aux

b = 6

a, b = b, a # 两个变量交换值，无需中间变量

b = 5

c = 5

else if x == 2: y = fun2(x)

else if x == 3: y = fun3(x)

else: y = None

elif x == 2: y = fun2(x)

elif x == 3: y = fun3(x)

else: y = None

# 但又时候，使用字典无疑更好些:

funs = {1: fun1, 2: fun2, 3: fun3}

y = funs.get(x, lambda x:None)(x)

for key in mapping.iterkeys(): ...

for key in mapping: ...

for i in xrange(len(al)):

print al[i]

for el in al:

print el

for i in xrange(len(al)-1, -1, -1):

print al[i]

for el in reversed(al):

print el

def __init__(I, x): ...

def __init__(self, x): ...

def sum_of(x, y, z): ...

"""Compute the sum of the ..."""

sl = ["ab", "cd", "ef"]

all = ""

for s in sl:

all += s

# Or:

sl = ["ab", "cd", "ef"]

all = reduce(lambda x,y: x+y, sl, "")

all = "".join(sl)

a = a.replace("‘", " ")

a = a.replace(".", " ")

a = a.replace("?", " ")

a = a.replace(",", "")

from string import maketrans

tab = maketrans("‘.?", "   ")

a = "this isn‘t a word, right."

afilt = a.translate(tab, ",")

l = [2, 3]

print apply(mul, l)

return x * y

l = [2, 3]

print mul(*l)

result = []

for el in vals:

if el > 0:

result.append(el * el)

result = [el * el for el in vals if el > 0]

m = [l] * 4

m[1][1] = 5

print m

m = [[0] * 4 for _ in xrange(4)]

m[1][1] = 5

print m

print a / 2, a / float(2)

from __future__ import division

a = 1

print a // 2, a / 2

def __init__(self, x, y, z):

self.x_public = x

self.y_private = y

self.z_veryprivate = z

def getx(self):

return self.x_public

print Foo(1, 2, 3).getx()

# Instance names starting with _ are meant as

# ‘to not mess with‘ by convention.

# Instance names starting with __ are private

# and receive name mangling.

class Foo(object):

def __init__(self, x, y, z):

self.x_public = x

self._y_private = y

self.__z_veryprivate = z

print Foo(1, 2, 3).x_public

\s*,\s*([-+]?\d+)\s*([\[\]])\s*$")

^ \s*             # start at beginning+ opt spaces

( [\[\]] )        # Group 1: opening bracket

\s*           # optional spaces

( [-+]? \d+ ) # Group 2: first number

\s* , \s*     # opt spaces+ comma+ opt spaces

( [-+]? \d+ ) # Group 3: second number

\s*           # opt spaces

( [\[\]] )        # Group 4: closing bracket

\s* $             # opt spaces+ end at the end

""", flags=re.VERBOSE)

# 上面的关于正则表达式代码就很容易读懂.

# 每行就像代码一样.

# 下面是另外一个不错的关于正则表达式排版方式:

spaces = r"\s*"            # optional spaces

number = r"( [-+]? \d+ )"  # Group

bracket = r"( [\[\]] )"    # Group. Closing bracket

parts = ["^", bracket, number, ",", number, bracket, "$"]

finder = re.compile(spaces.join(parts), flags=re.VERBOSE)

"""A comment"""

...implementation...

def function(data):

"""A comment

>>> function()

None

>>> function(1)

result1

>>> function("a")

Traceback (most recent call last):

...

TypeError

"""

...implementation...

if __name__ == "__main__":

import doctest

doctest.testmod()

print "Tests done."

301, 456, 958, 1256, \

1359, 2568, 3597)

301, 456, 958, 1256,

1359, 2568, 3597)

# 太多的行，必须用\来作为分割符

# 但\在() [] {}中是不必要的

from mymodule import *

from mymodule import fun1, Class1, baseconvert as bc

psyco.bind(myfun1)

a = [3.56, 2.12]

import psyco

# psyco中的类非常有用

from psyco.classes import __metaclass__

psyco.bind(myfun1)

except ImportError: pass

# 使用psyco array.array中

# 双精度值可以更快些

import array

a = array.array("d", [3.56, 2.12])

# 在一些情形下，使用字符串数组同样很快

# psyco同map,filter,生成器一起使用也会很慢 can be slow with itertools, map, filter

# 但会比列表解析快

# 最快的Psyco是使用低级别的编码格式

from sys import stdout

stdout.write(string1)

stdout.write(string2)

words = [‘me‘, ‘do‘ ‘bye‘, ‘taz‘, ‘foo‘, ‘bar‘]

A shorter, more readable, but slower alternative:

words = ‘me do bye taz foo bar‘.split()

# try to remove the i index from the temporary tuples

lp = [(5J,"b"),(2J,"c"),(3+1J,"a"),(1+2J,"a")]

lp2 = [(c, i, n) for i,(n, c) in enumerate(lp)]

lp2.sort()

print [(n, c) for (c, i, n) in lp2]

lp = [(5J, "b"), (2J, "c"), (3+1J, "a"), (1+2J, "a")]

print sorted(lp, key=itemgetter(1))

tot = -2.0

for v in vals:

tot += v

tot = sum(vals, -2.0)

print sum(ll, [])

result = []

for sublist in data:

result.extend(sublist)

# 最快速度实现

from itertools import imap

data = [[1, 2, 3], [4], [5, 6]]

result = [None] * sum(imap(len, data))

pos = 0

for sublist in data:

lensl = len(sublist)

result[pos : pos+lensl] = sublist

pos += lensl

print ‘"‘ + chr(c) + ‘":‘, freq[c]

print ‘"%c": %d‘ % (c, freq[c])

(c if c.isalpha() else ‘ ‘)

alist[::-1]

astring[::-1]

#  element of alist:

result = []

for (i, v) in enumerate(alist):

# faster than i % 2

if i & 1 == 0:

result.append(v)

else:

result.append(-v)

alist[:] = result

alist[1::2] = map(neg, alist[1::2])

# 下面方式虽慢点，但是易读:

alist[1::2] = [-el for el in alist[1::2]]

# (元祖无需拷贝)

newlist = list(alist)

newdict = dict(adict)

# 或者仅仅是:

newlist = list[:]

sys.exit()

raise SystemExit

#或者仅仅是:

exit()

if type(seq) == list or \

type(seq) == tuple: ...

if isinstance(seq, (list, tuple)): ...

# Or even:

if hasattr(seq, "__getitem__"): ...

# But quite often in dynamic languages you

# don‘t test types, you just use them (look

# for duck typing), catching exception that

# may occur.

a = 1

b = 2

c = 3

name2 = 20

print name2

a, b, c = 1, 2, 3

rossa = "Il colore rosso"

léger = 30

first = 1

red = "Il colore rosso"

light = 30

usually left undefined.

fin = file("absent_file.txt")

except:

...

try:

something()

except:

...

try:

fin = file("absent_file.txt")

except IOError:

...

try:

something()

except someException:

...

# 或者:

from itertools import repeat

bytes = array.array(‘B‘, repeat(0, nbytes))

bytes = array.array(‘B‘, [0]) * nbytes

for c in "abracadabra":

try:

freqs[c] += 1

except:

freqs[c] = 1

freqs = {}

for c in "abracadabra":

freqs[c] = freqs.get(c, 0) + 1

# 常用方式:

freqs = {}

for c in "abracadabra":

if c in freqs:

freqs[c] += 1

else:

freqs[c] = 1

# 或者在Python 2.5以上版本使用:

from collections import defaultdict

freqs = defaultdict(int)

for c in "abracadabra":

freqs[c] += 1

somemap = {1:2, 3:4, 5:6}

print list(someitems)[0]

print list(somemap)[0]

somemap = {1: 2, 3: 4, 5: 6}

print iter(someitems).next()

print iter(somemap).next()

from timeit import default_timer as clock

# 或者经常使用timeit模块来计算程序运行时间