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python 编码规范及习惯写法范例

2014-08-19 18:13 260 查看
python代码习惯写法：转自 http://www.fantascienza.net/leonardo/ar/python_best_practices.html
python代码编写过程中有一些习惯写法，Bad和Good是对相同代码的不同表示，其中Good是python中通用的代码编写规范。

[align=center]Bad[/align]
[align=center]Good[/align]
x=5

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

1<<5&2

return(5);

while (x<5) : ...

7. 		x = 5

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

(1 << 5) & 2

return 5

while x < 5: ...

7.0
print x,x*x+1

v[i + 1 + a] + v[i + 2 + b]		# Sometimes rules can be broken, for

# example to show grouping better:

print x, x*x + 1

v[i+a+1] + v[i+b+2]
def Function ( x ): ...def function(x): ...
class fooclass: ...class Fooclass(object): ...
d = dict()freqs = {}

# Descriptive names are often better

# But in small scopes a short name may be fine
list = [1, 2, 3]

dict = {'alpha': 0x1234}

sum = x + y 		# Don't shadow builtin names

values = [1, 2, 3]

symbol_address = {'alpha': 0x1234}

tot = x + y
"some string" and 'some string' and

"""some string""" and '''some string'''

are the same string.
mapping = { 5 :"5", 6:"6" }mapping = {5: "5", 6: "6"}
mapping = {5 : "5", 6 : "6"}

if mapping.has_key(6): ...		mapping = {5: "5", 6: "6"}

if 6 in mapping: ...
def function( x, l = [] ): ...# Generally don't use mutables as a default

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

if items is None:

items = []
if x == None: ...if x is None: ...
x = 1

if z > 5:

var1 = 55		# Always use 4 spaces as indent

# (Or always a Tab, but it's less good)

x = 1

if z > 5:

var1 = 55
mapping = {5 : "5", 6 : "6"}

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

for key in mapping.keys(): ...		# Use iter* methods when possible

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

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

for key in mapping: ...
for i in range(10, 20000): ...for i in xrange(10, 20000): ...
# Use to denote the code that has to

# run when a module is executed and not

# imported:

if __name__ == '__main__':
# Python profiler:

python -m profile -o stats myscript.py

>>> import pstats

>>> p = pstats.Stats('stats')

>>> p.sort_stats('time').print_stats(15)
For source code with not 7-bit ASCII

add this on top:

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

# Or just, if you have less memory:

# coding: latin
al = [1, 2, 3]

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

del al[i]		items = [1, 2, 3]

del items[:]

# But often if speed isn't critical you

# can just use (but this is a different

# thing, this creates a new list):

items = []

# If you just want to remove one refence

# to the list:

del items
repeat

xxx

until yyy		# Equals to:

while True

xxx

if yyy: break
# To add a zip file containing modules

# to the search path:

sys.path.append("some.zip")
a = 5

b = 6

aux = a

a = b

b = aux

a = 5

b = 6

a, b = b, a # swap
if x < 10 and x > 2: ...if 2 < x < 10: ...
a = 5

b = 5

c = 5		a = b = c = 5
if x == 1: y = fun1(x)

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

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

else: y = None		if x == 1: y = fun1(x)

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

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

else: y = None

# But sometimes a dict is better:

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

y = funs.get(x, lambda x:None)(x)
mapping = {5 : "5", 6 : "6"}

for key in mapping.iterkeys(): ...		mapping = {5: "5", 6: "6"}

for key in mapping: ...
al = [1, 2, 3]

for i in xrange(len(al)):

print al[i]		al = [1, 2, 3]

for el in al:

print el
al = [1, 2, 3]

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

print al[i]		al = [1, 2, 3]

for el in reversed(al):

print el
class Test(object):

def __init__(I, x): ...		class Test(object):

def __init__(self, x): ...
# Compute the sum of the ...

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

"""Compute the sum of the ..."""
from operator import add

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

all = ""

for s in sl:

all += s

# Or:

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

all = reduce(lambda x,y: x+y, sl, "") 		sl = ["ab", "cd", "ef"]

all = "".join(sl)
a = "this isn't a word, right?"

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

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

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

a = a.replace(",", "")		# .replace can be fine. This is faster:

from string import maketrans

tab = maketrans("'.?", " ")

a = "this isn't a word, right."

afilt = a.translate(tab, ",")
values = ["stop",0,0]values = ["stop", 0, 0]
def mul(x, y): return x*y

l = [2, 3]

print apply(mul, l)		def mul(x, y):

return x * y

l = [2, 3]

print mul(*l)
vals = [2, 3, -5, 0]

result = []

for el in vals:

if el > 0:

result.append(el * el) 		vals = [2, 3, -5, 0]

result = [el * el for el in vals if el > 0]
l = [0] * 4

m = [l] * 4

m[1][1] = 5

print m		# One correct way to create a matrix:

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

m[1][1] = 5

print m
a = 1

print a / 2, a / float(2)		# A kind of alternative:

from __future__ import division

a = 1

print a // 2, a / 2
class Foo(object):

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()		# Generally getters and setters are not used.

# 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

finder = re.compile("^\s*([\[\]])\s*([-+]?\d+)

\s*,\s*([-+]?\d+)\s*([\[\]])\s*$")		finder = re.compile(r"""

^ \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)

# Sometimes it's positive to indent logically those

# lines just like code.

# Sometimes it can be positive to compose REs:

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)
def function(data):

"""A comment"""

...implementation...		# Use doctests (or module tests):

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."

x = (1, 2, 6, 55, 63, 96, 125, 256, \

301, 456, 958, 1256, \

1359, 2568, 3597)		x = (1, 2, 6, 55, 63, 96, 125, 256,

301, 456, 958, 1256,

1359, 2568, 3597)

# Too much long lines must be broken with \

# but \ isn't necessary inside () [] {}
from Tkinter import *

from mymodule import *		import Tkinter as tk

from mymodule import fun1, Class1, baseconvert as bc
import psyco

psyco.bind(myfun1)

a = [3.56, 2.12]		try:

import psyco

# Psyco classes may be very useful

from psyco.classes import __metaclass__

psyco.bind(myfun1)

except ImportError: pass

# Using psyco array.array of double and

# signed long become very fast

import array

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

# In some situations arrays of chars too are fast

# psyco can be slow with itertools, map, filter

# and generators, but fast with list

# comprehensions. For max speed with Psyco

# use low level coding style.
# to print strings without spaces between:

from sys import stdout

stdout.write(string1)

stdout.write(string2)
This is good enough:

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

A shorter, more readable, but slower alternative:

words = 'me do bye taz foo bar'.split()
# sorting on the second item of the tuple

# 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]		from operator import itemgetter

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

print sorted(lp, key=itemgetter(1))
vals = [5, 7 ,8]

tot = -2.0

for v in vals:

tot += v		vals = [5, 7 ,8]

tot = sum(vals, -2.0)
ll = [[1, 2, 3], [4], [5, 6]]

print sum(ll, [])		data = [[1, 2, 3], [4], [5, 6]]

result = []

for sublist in data:

result.extend(sublist)

# Or even, for max speed

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 "%s %s" % (string1, string2)

print '"' + chr(c) + '":', freq[c]		print string1, string2

print '"%c": %d' % (c, freq[c])
[' ', c][c.isalpha()]# For Python V.2.5+:

(c if c.isalpha() else ' ')
# How to invert string, lists, etc.

alist[::-1]

astring[::-1]
# To negate (inplace) each second

# 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		from operator import neg

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

# Or a bit slower but easier to read:

alist[1::2] = [-el for el in alist[1::2]]
# To shallow copy a list or dict:

# (tuples don't need to be copied)

newlist = list(alist)

newdict = dict(adict)

# Or just:

newlist = list[:]
import sys

sys.exit()		# To stop a console program:

raise SystemExit

#Or just:

exit()
if type(s) == type(""): ...

if type(seq) == list or \

type(seq) == tuple: ...		if isinstance(s, basestring): ...

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.
name1 = 5; name2 = 20; print name2

a = 1

b = 2

c = 3		name1 = 5

name2 = 20

print name2

a, b, c = 1, 2, 3
prima = 1

rossa = "Il colore rosso"

léger = 30		# English only for names:

first = 1

red = "Il colore rosso"

light = 30
__del__ method of classes is

usually left undefined.
try:

fin = file("absent_file.txt")

except:

...

try:

something()

except:

...		# Generally specify what exception to catch:

try:

fin = file("absent_file.txt")

except IOError:

...

try:

something()

except someException:

...
except ImportError, IOError: ...except (ImportError, IOError): ...
bytes = array.array('B', [0] * nbytes)

# Or:

from itertools import repeat

bytes = array.array('B', repeat(0, nbytes))		# This can be much faster

bytes = array.array('B', [0]) * nbytes
freqs = {}

for c in "abracadabra":

try:

freqs[c] += 1

except:

freqs[c] = 1		# Short way:

freqs = {}

for c in "abracadabra":

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

# Often the fastest way:

freqs = {}

for c in "abracadabra":

if c in freqs:

freqs[c] += 1

else:

freqs[c] = 1

# Or better with Python 2.5+:

from collections import defaultdict

freqs = defaultdict(int)

for c in "abracadabra":

freqs[c] += 1
someitems = set([1, 2, 3])

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

print list(someitems)[0]

print list(somemap)[0]

someitems = set([1, 2, 3])

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

print iter(someitems).next()

print iter(somemap).next()
from time import clock# This works well on Windows and Linux:

from timeit import default_timer as clock

# Or often use the timeit module
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