这就是菜鸟和高手的区别！完全不同的两个世界！Python必然会爆火

进群：548377875 ?都可以获取到不同的PDF哦！是非常实用的PDF哦！

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  and :
 # do something

Pythonic

print 'one'
print 'two'
if x == 1:
 print 'one'
cond1 = 
cond2 = 
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 = [1,3,4]
# 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','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 = [3,5]
b = [i for i in a if i > 4]
# Or:
b = filter(lambda x: x > 4,a)

Bad

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

Pythonic

a = [3,5]
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,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

（编辑：李大同）

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