7C00.ME/houmu 2014-06-25

[转载]符合语言习惯的python编程

转自:http://xiaocong.github.io/slides/idiomatic-python-code/#/main

PEP 8: Style Guide for Python Code http://www.python.org/dev/peps/pep-0008/

交换赋值

不推荐

temp = a
a = b
b = a

推荐

a, b = b, a # 先生成一个元组(tuple)对象,然后unpack

Unpacking

不推荐

l = ['David', 'Pythonista', '+1-514-555-1234']
first_name = l[0]
last_name = l[1]
phone_number = l[2]

推荐

l = ['David', 'Pythonista', '+1-514-555-1234']
first_name, last_name, phone_number = 1

# Python 3 Only
firs, *middle, last = another_list

使用操作符in

不推荐

if fruit == "apple" or fruit == "orange" or fruit == "berry":
    # 多次判断

推荐 python if fruit in ["apple", "orange", "berry"]: # 使用 in 更简洁

字符串操作

不推荐

colors = ['red', 'blue', 'green', 'yellow']

result = ''
for s = in colors:
    result += s # 每次赋值都丢弃以前的字符串对象,生成一个新对象

推荐

colors = ['red', 'blue', 'green', 'yellow']
result = ''.join(colors) # 没有额外的内存分配

### 字典键值列表

不推荐

for key in my_dict.keys():
    # my_dict[key] ...

推荐

for key in my_dict:
    # my_dict[key] ...

# 只有当循环中需要更改key值的情况下,我们需要使用my_dict.keys()
# 生成静态的键值列表。

### 字典键值判断

不推荐

if my_dict.has_key(key):
    # ...do something with d[key]

推荐

if key in my_dict:
    # ...do something with d[key]

字典 get 和 setdefault 方法

不推荐

navs = {}
for (portfolio, equity, position) in data:
    if portfolio not in navs:
        navs[portfolio] = 0
    navs[portfolio] += position * prices[equity]

推荐

navs = {}
for (portfolio, equity, position) in data:
    # 使用 get 方法
    navs[portfolio] = navs.get(portfolio, 0) + \
        position * prices[equity]
    # 或者使用 setdefault 方法
    navs.setdefault(portfolio, 0)
    navs[portfolio] += position * prices[equity]

### 判断真伪

不推荐

if x == True:
    # ...
if len(items) != 0:
    # ...
if items != []:
    # ...

推荐

if x:
    # ...
if items:
    # ...

### 遍历列表以及索引

不推荐

items = 'zero one two three'.split()
# method 1
i = 0
for item in items:
    print i, item
    i += 1
# method 2
for i in range(len(items)):
    print i, items[i]

推荐

items = 'zero one two three'.split()
for i, item in enumerate(items):
    print i, item

列表推导

不推荐

new_list = []
for item in a_list:
    if condition(item):
        new_list.append(fn(item))

推荐

new_list = [fn(item) for item in a_list if condition(item)]

列表推导-嵌套

不推荐

for sub_list in nested_list:
    if list_condition(sub_list):
        for item in sub_list:
            if item_condition(item):
                # do something ...

推荐

gen = (item for sl in nested_list if list_condition(sl) \
    for item in sl if item_condition(item))
for item in gen:
    # do something...

循环嵌套

不推荐

for x in x_list:
    for y in y_list:
        for z in z_list:
            # do something for x & y

推荐

from itertools import product
for x, y, z in product(x_list, y_list, z_list):
    # do something for x, y, z

### 尽量使用生成器代替列表

不推荐

def my_range(n):
    i = 0
    result = []
    while i < n:
        result.append(fn(i))
        i += 1
    return result # 返回列表

推荐

def my_range(n):
    i = 0
    result = []
    while i < n:
        yield fn(i) 使用生成器代替列表
        i += 1

尽量使用生成器代替列表,除非必须用到列表特有的函数

中间结果尽量使用 imap/ifilter 代替 map/filter

不推荐

reduce(rf, filter(ff, map(mf, a_list)))

推荐

from itertools import ifilter, imap
reduce(rf, ifilter(ff, imap(mf, a_list)))

使用 any/all 函数

不推荐

found = False
for item in a_list:
    if condition(item):
        found = True
        break
if found:
    # do something if found

推荐

if any(condition(item) for item in a_list):
    # do something if found

### 属性 (property)

不推荐

class Clock(object):
    def __init__(self):
        self.__hour = 1
    def setHour(self, hour):
        if 25 > hour > 0 : self.__hour = hour
        else: raise BadHourException
    def getHour(self):
        return self.__hour

推荐

class Clock(object):
    def __init__(self):
        self.__hour = 1
    def __setHour(self, hour):
        if 25 > hour > 0 : self.__hour = hour
        else: raise BadHourException
    def __getHour(self):
        return self.__hour
    hour = property(__getHour, __setHour)

使用 with 处理文件打开

不推荐

f = open("some_file.txt")
try:
    data = f.read()
    # 其他文件操作
finally:
    f.close()

推荐

with open("some_file.txt") as f:
    data = f.read()
    # 其他文件操作

使用 with 忽略异常 (仅限 Python 3)

不推荐

try:
    os.remove("somefile.txt")
except OSError:
    pass

推荐

from contextlib import ignored

with ignored(OSError):
    os.remove("somefile.txt")

使用 with 处理加锁

不推荐

import threading
lock = threading.Lock()

lock.acquire()
try: 
    # 互斥操作
finally:
    lock.release()

推荐

import threading
lock = threading.Lock()

with lock:
    # 互斥操作

参考