Python的十种惯用法

十种Python惯用法，可以让你的代码更Pythonic

让脚本同时具有可引用性和可独立执行性

if __name__ == '__main__':

def main():
	printf('Doing stuff in module',__name__)

if __name == '__main__':
	printf('Executed from the command line')
	main()

可同时在控制台下直接执行，也可以以模块的形式导入后引用
import mymodule
mymodule.main()

检查逻辑布尔值

if x:
if not x:

#GOOD
name = 'Safe'
pets = ['Dog','Cat','Hamster']
owners = {'Safe': 'Cat','George': 'Dog'}
if name and pets and owners:
	printf('We have pets')

#NOT SO GOOD
if name != '' and len(pets) > 0 and owners != {}:
	print('We have pets')

尽可能的使用in

Contains:
if x in items:
Iteration:
for x in intems:

#GOOD
name = 'Safe Hammad'
if 'H' in name:
	print('This name has an H in it!')

#NOT SO GOOD
name ='Safe Hammad'
if name.find('H') != -1:
	print('This name has an H in it!')

#GOOD
pets = ['Dog','Cat','Hanster']
for pet in perts:
	print('A',pet,'can be very cute!')

#NOT SO GOOD
pets = ['Dog','Cat','Hanster']
i = 0 
while i < len(pets):
	print ('A',pets[i],'can be very cute!')
	i += 1

使用in可以清楚，精确的检查一个项目是否在一个序列中
可以在list,dicts(keys)，sets,strings使用，还可在实现的__contains__方法的类中使用

不用临时变量交换两值

a,b = b,a

#GOOD
a,b = 5,6
print a,b #5,6
a,b = b,a
print a,b #6,5
#NOT SO GOOD
a,b = 5,6
print a,b

temp =a
a = b
b = temp
print a,b # 6,5

避免仅使用一次的temp变量使得命名空间变复杂

使用sequence建立字串

''.join(some_strings)

#GOOD 
chars = ['s','a','f','e']
name = ''.join(chars)
print name #Safe

#NOT SO GOOD
chars = ['s','a','f','e']
name = ''
for char in chars:
	name += char

print name #Safe

join开销是线性时间，+开销是平方使用

EAFP 胜于 LBYL

“it’s Easier to Ask for Forgiveness than Permission.”
“Look Before You Leap”
try:
except:

#GOOD
d = {'X':'5'}
try:
	value = int(d['x'])
except (KeyError,TypeError,ValueError):
	value = None

#NOT SO GOOD
d = {'x':'5'}
if 'x' in d and  is instance(d['x'],str) and d['x'].isdigit():
	value = int(d['x'])
else:
	value = None

在pyhton中抛出异常没有java中那么开销大
Rely on duck typing rather than checking for a specific type

enumerate方法

for i,item in enumerate(items):

#GOOD
names = ['Safe','George','Mildred']
for i,name in enumerate(names):
	print(i,name) #0 Safe,1 George etc.

#NOT SO GOOD
names = ['Safe','George','Mildred']
count = 0
for name in names:
	print(i,name) #0 Safe,1 George etc.
	count += 1

Python2.3+版本都支持enumerate方法
Python2.6支持使用参数指定从非0位置开始计数

使用列表推导式建立列表

[i * 3 for i in data if i> 10]

#GOOD
data = [7,20,3,15,11]
result = [i * 3 for i in data if i > 10]
print result #[60,45,33]

#NOT SO GOOD
data = [7,20,3,15,11]
result = []
for i in data:
	if i>10:
		result.append(i * 3)
print result #[60,45,33]

谨慎使用列表推导式，有些情况会使情况变的更复杂，第二种用法反而更明朗清晰

通过键值对建立dict数据结构时使用zip

d = dict(zip(keys,values))

#GOOD
keys = ['Safe','Bob','Thomas']
values = ['Hammad','Builder','Engine']
d = dict(zip(keys,values))
print d #{'Bob':'Builder','Safe':'Hammad','Thomas':'Engine'}

#NOT SO GOOD
keys = ['Safe','Bob','Thomas']
values = ['Hammad','Builder','Engine']
d = {}
for i,key in enumerate(keys):
	d[keys] = values[i]
print d #{'Bob':'Builder','Safe':'Hammad','Thomas':'Engine'}

其它

参看资料