列表解析式

没有列表解析式的情况下:

x = []
for i in (1,2,3):
	x.append(i)
print x

返回：
[1, 2, 3]

使用列表解析式的实现:

>>> x = [i for i in (1,2,3)]
>>> x
[1, 2, 3]
x = [word.capitalize() for line in ('hello world?','world!','or not')
for word in line.split()
if not word.startswith('or')]

print x

# 返回
['Hello', 'World?', 'World!', 'Not']

字典解析式

In [18]: {x:x.upper() for x in ['hello',' world']}
Out[18]: {' world': ' WORLD', 'hello': 'HELLO'}
In [19]: {x.upper() for x in ['hello','world']}
Out[19]: {'HELLO', 'WORLD'}
In [24]: word = 'letter'

In [25]: letter_counts = {letter: word.count(letter) for letter in set(word)}

In [26]: letter_counts
Out[26]: {'e': 2, 'l': 1, 'r': 1, 't': 2}

集合解析式

In [24]: a= {x.upper() for x in ['hello','world']}

In [25]: print a
set(['WORLD', 'HELLO'])

enumerate

enumerate(sequence, start=0)

返回一个可迭代enumerate对象，它生成一个元组序列，

不用 enumerate的写法:

i = 0
mylist = ['first','two','three']
while i < len(mylist):
	print("Item %d: %s:" % (i,mylist[i]))
	i +=1

# 返回
Item 0: first:
Item 1: two:
Item 2: three:

enumerate写法

mylist = ['first','two','three']

for i,item in enumerate(mylist):
	print("Item %d: %s" % (i,item))

# 返回
Item 0: first
Item 1: two
Item 2: three

item为列表中的元素

。