一十九条优雅Python编程技巧

1.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，然后在unpack

2.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 = l
 #python 3 only
 first, *middle, last = another_list

3.使用操作符in

 #不推荐
 if fruit = "apple" or fruit == "orange" or fruit == "berry":
         #多次判断
 #推荐
 if fruit in ["apple","orange","berry"]:
         #使用in更加简洁

4.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

5.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

6.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]

7.字典 get 和 setdefault 方法

 #不推荐
 navs = {}
 for (portfolio, equity, position) in data:
 　　if portfolio not in navs:
 5 　　　　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]

8.判断真伪

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

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

9.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

10.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)]

11.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 s1 in nested_list if list_condition(s1) \
                   for item in s1 if item_condition(item))
 for item in gen:
     #do something

12.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

13.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  #返回值

 #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

 #【尽量用生成器代替列表，除非必须用到列表特有的函数】

14.中间结果尽量使用 imap/ifilter 代替 map/filter

 #不推荐
 reduce(rf, filiter(ff, map(my, a_list)))

 #推荐
 from itertools import ifilter,imap
 reduce(rf, ifilter(ff, imap(mf, a_list)))
 #【lazy evaluation 会带来更高的内存使用效率，特别是当处理大数据操作的时候】

15.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...

16.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 BadHour Exception
     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 BadHour Exception
     def __getHour(self):
         return self.__hour
     hour = property(__getHour,__setHour)

17.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 ...

18.使用 with 忽视异常（仅限Python 3）

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

 #推荐
 from contextlib import ignored   #python 3 only

 with ignored(OSError):
     os.remove("something.txt')

19.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 ...