Python【15个代码示例】

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，这里收集了一些常见的 Pythonic 写法，帮助你养成写优秀代码的习惯。

Python

变量交换

tmp = a
a = b
b = tmp

Pythonic

a,b = b,a

列表推导

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

Pythonic

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

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。

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

带索引遍历

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

Pythonic

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

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
1

字符串拼接

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

Pythonic

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

真假判断

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!'

访问字典元素

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']

操作列表

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)

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)

文件读取

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

Pythonic

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

代码续行

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)

显式代码

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

Pythonic

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

使用占位符

Pythonic

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

链式比较

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

三目运算

这个保留意见。随使用习惯就好。

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

Pythonic

a = 3

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