15个Pythonic的代码示例(值得收藏)

python由于语言的简洁性，让我们以人类思考的方式来写代码，新手更容易上手，老鸟更爱不释手。

要写出 pythonic（优雅的、地道的、整洁的）代码，还要平时多观察那些大牛代码，github 上有很多非常优秀的源代码值得阅读，比如：requests、flask、tornado，这里小明收集了一些常见的 pythonic 写法，帮助你养成写优秀代码的习惯。

01. 变量交换

bad

tmp = a
a = b
b = tmp

pythonic

a,b = b,a

02. 列表推导

bad

my_list = []
for i in range(10):
  my_list.append(i*2)

pythonic

my_list = [i*2 for i in range(10)]

03. 单行表达式

虽然列表推导式由于其简洁性及表达性，被广受推崇。

但是有许多可以写成单行的表达式，并不是好的做法。

bad

print 'one'; print 'two'

if x == 1: print 'one'

if <complex comparison> and <other complex comparison>:
  # do something

pythonic

print 'one'
print 'two'

if x == 1:
  print 'one'

cond1 = <complex comparison>
cond2 = <other complex comparison>
if cond1 and cond2:
  # do something

04. 带索引遍历

bad

for i in range(len(my_list)):
  print(i, "-->", my_list[i])

pythonic

for i,item in enumerate(my_list):
  print(i, "-->",item)

05. 序列解包

pythonic

a, *rest = [1, 2, 3]
# a = 1, rest = [2, 3]

a, *middle, c = [1, 2, 3, 4]
# a = 1, middle = [2, 3], c = 4

06. 字符串拼接

bad

letters = ['s', 'p', 'a', 'm']
s=""
for let in letters:
  s += let

pythonic

letters = ['s', 'p', 'a', 'm']
word = ''.join(letters)

07. 真假判断

bad

if attr == true:
  print 'true!'

if attr == none:
  print 'attr is none!'

pythonic

if attr:
  print 'attr is truthy!'

if not attr:
  print 'attr is falsey!'

if attr is none:
  print 'attr is none!'

08. 访问字典元素

bad

d = {'hello': 'world'}
if d.has_key('hello'):
  print d['hello']  # prints 'world'
else:
  print 'default_value'

pythonic

d = {'hello': 'world'}

print d.get('hello', 'default_value') # prints 'world'
print d.get('thingy', 'default_value') # prints 'default_value'

# or:
if 'hello' in d:
  print d['hello']

09. 操作列表

bad

a = [3, 4, 5]
b = []
for i in a:
  if i > 4:
    b.append(i)

pythonic

a = [3, 4, 5]
b = [i for i in a if i > 4]
# or:
b = filter(lambda x: x > 4, a)

bad

a = [3, 4, 5]
for i in range(len(a)):
  a[i] += 3

pythonic

a = [3, 4, 5]
a = [i + 3 for i in a]
# or:
a = map(lambda i: i + 3, a)

10. 文件读取

bad

f = open('file.txt')
a = f.read()
print a
f.close() 

pythonic

with open('file.txt') as f:
  for line in f:
    print line 

11. 代码续行

bad

my_very_big_string = """for a long time i used to go to bed early. sometimes, \
  when i had put out my candle, my eyes would close so quickly that i had not even \
  time to say “i'm going to sleep.”"""

from some.deep.module.inside.a.module import a_nice_function, another_nice_function, \
  yet_another_nice_function 

pythonic

my_very_big_string = (
  "for a long time i used to go to bed early. sometimes, "
  "when i had put out my candle, my eyes would close so quickly "
  "that i had not even time to say “i'm going to sleep.”"
)

from some.deep.module.inside.a.module import (
  a_nice_function, another_nice_function, yet_another_nice_function) 

12. 显式代码

bad

def make_complex(*args):
  x, y = args
  return dict(**locals())

pythonic

def make_complex(x, y):
  return {'x': x, 'y': y}

13. 使用占位符

pythonic

filename = 'foobar.txt'
basename, _, ext = filename.rpartition('.')

14. 链式比较

bad

if age > 18 and age < 60:
  print("young man")

pythonic

if 18 < age < 60:
  print("young man")

理解了链式比较操作，那么你应该知道为什么下面这行代码输出的结果是 false

>>> false == false == true 
false

15. 三目运算

这个保留意见。随使用习惯就好。

bad

if a > 2:
  b = 2
else:
  b = 1
#b = 2

pythonic

a = 3  

b = 2 if a > 2 else 1
#b = 2 

参考文档

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