学习笔记
#python 3.5.2
解压序列赋值给多个变量
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>>> x=(1,2,3)
>>> a,b,c=x
>>> a
1
>>> b
2
>>> c
3
>>> data=[
'1'
,
'2'
,
'3'
,
'4'
,
'5'
]
>>> _,a,_,_,b=data
>>> a
'2'
>>> b
'5'
>>> y=(3,4)
>>> a,b,c=y
Traceback (most recent call last):
File
"<pyshell#14>"
, line 1,
in
<module>
a,b,c=y
ValueError: not enough values to unpack (expected 3, got 2)
>>>
>>> data=[
'1'
,2,(3,4),5]
>>> a,b,L,c=data
>>> L
(3, 4)
>>> a
'1'
>>> c
5
>>>
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解压可迭代对象赋值给多个变量
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>>> L=[1,2,3,4,5,6]
>>>
head
,*
tail
=L
>>>
head
1
>>>
tail
[2, 3, 4, 5, 6]
>>>
head
,*middle,
tail
=L
>>>
head
1
>>> middle
[2, 3, 4, 5]
>>>
tail
6
>>> L=[
'aaa'
,10,(1,2,3),
'dddd'
]
>>>
head
,*middle,
tail
=L
>>>
head
'aaa'
>>> middle
[10, (1, 2, 3)]
>>>
tail
'dddd'
>>> name,age,(a,b,c),addr=L
>>> a
1
>>> b
2
>>> c
3
>>> addr
'dddd'
>>> age
10
>>>
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保留最后N个元素
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>>> from collections
import
deque
>>> q=deque(maxlen=4)
>>> q.append(1)
>>> q.append(2)
>>> q.append(3)
>>> q
deque([1, 2, 3], maxlen=4)
>>> q.append(4)
>>> q
deque([1, 2, 3, 4], maxlen=4)
>>> q.append(5)
>>> q
deque([2, 3, 4, 5], maxlen=4)
>>> q.append(6)
>>> q
deque([3, 4, 5, 6], maxlen=4)
>>> q.appendleft(0)
>>> q
deque([0, 3, 4, 5], maxlen=4)
>>> q.appendleft(-1)
>>> q
deque([-1, 0, 3, 4], maxlen=4)
>>>
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查找最大或最小的N个元素
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>>>
import
heapq
>>> nums = [1, 8, 2, 23, 7, -4, 18, 23, 42, 37, 2]
>>> heapq.nlargest(3,nums)
[42, 37, 23]
>>> heapq.nlargest(4,nums)
[42, 37, 23, 23]
>>> heapq.nsmallest(2,nums)
[-4, 1]
>>> heapq.nsmallest(4,nums)
[-4, 1, 2, 2]
>>>
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实现一个优先级队列
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>>>
import
heapq
>>> queue=[]
>>> heapq.heappush(queue,(3,
'three'
))
>>> heapq.heappush(queue,(2,
'two'
))
>>> heapq.heappush(queue,(5,
'five'
))
>>> heapq.heappush(queue,(1,
'one'
))
>>> heapq.heappush(queue,(4,
'four'
))
>>> heapq.heappop(queue)
(1,
'one'
)
>>> heapq.heappop(queue)
(2,
'two'
)
>>> heapq.heappop(queue)
(3,
'three'
)
>>> heapq.heappop(queue)
(4,
'four'
)
>>> heapq.heappop(queue)
(5,
'five'
)
>>>
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字典中键映射多个值
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>>> from collections
import
defaultdict
>>> d=defaultdict(list)
>>> d[
'a'
].append(1)
>>> d[
'a'
].append(2)
>>> d[
'a'
].append(3)
>>> d[
'b'
].append(-1)
>>> d[
'b'
].append(-2)
>>> d[
'c'
].append(
'C'
)
>>> d
defaultdict(<class
'list'
>, {
'b'
: [-1, -2],
'c'
: [
'C'
],
'a'
: [1, 2, 3]})
>>>
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字典保持顺序
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>>> from collections
import
OrderedDict
>>> d=OrderedDict()
>>> d[
'B'
]=2
>>> d[
'A'
]=1
>>> d[
'C'
]=3
>>> d[
'F'
]=6
>>> d[
'E'
]=5
>>> d
OrderedDict([(
'B'
, 2), (
'A'
, 1), (
'C'
, 3), (
'F'
, 6), (
'E'
, 5)])
>>>
for
i
in
d:
print(i,d[i])
B 2
A 1
C 3
F 6
E 5
>>> D=dict()
>>> D[
'B'
]=2
>>> D[
'A'
]=1
>>> D[
'C'
]=3
>>> D[
'F'
]=6
>>> D[
'E'
]=5
>>>
for
i
in
D:
print(i,D[i])
A 1
F 6
C 3
B 2
E 5
>>>
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字典的运算
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>>> prices = {
'ACME'
: 45.23,
'AAPL'
: 612.78,
'IBM'
: 205.55,
'HPQ'
: 37.20,
'FB'
: 10.75
}
>>> min_price=min(zip(prices.values(),prices.keys()))
>>> min_price
(10.75,
'FB'
)
>>> max_price=max(zip(prices.values(),prices.keys()))
>>> max_price
(612.78,
'AAPL'
)
>>> prices_sorted=sorted(zip(prices.values(),prices.keys()))
>>> prices_sorted
[(10.75,
'FB'
), (37.2,
'HPQ'
), (45.23,
'ACME'
), (205.55,
'IBM'
), (612.78,
'AAPL'
)]
>>> min(prices)
'AAPL'
>>> max(prices)
'IBM'
>>> min(prices,key=lambda x:prices[x])
'FB'
>>> max(prices,key=lambda x:prices[x])
'AAPL'
>>> prices[min(prices,key=lambda x:prices[x])]
10.75
>>> prices[max(prices,key=lambda x:prices[x])]
612.78
>>>
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查找两个字典的相同点
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>>> a = {
'x'
: 1,
'y'
: 2,
'z'
: 3
}
>>> b = {
'w'
: 10,
'x'
: 11,
'y'
: 2
}
>>> a.keys() & b.keys()
{
'x'
,
'y'
}
>>> a.keys() - b.keys()
{
'z'
}
>>> a.items() & b.items()
{(
'y'
, 2)}
>>>
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删除序列相同元素并保持顺序
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>>> def dedupe(items):
seen =
set
()
for
item
in
items:
if
item not
in
seen:
yield item
seen.add(item)
>>> a = [1, 5, 2, 1, 9, 1, 5, 10]
>>> list(dedupe(a))
[1, 5, 2, 9, 10]
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>>>
命名切片
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>>> record =
'....................100 .......513.25 ..........'
>>> shares=slice(20,23)
>>> price=slice(31,37)
>>> cost=int(record[shares])*float(record[price])
>>> cost
51325.0
>>>
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本文转自 chaunceyjiang 51CTO博客，原文链接：http://blog.51cto.com/cqwujiang/1948892，如需转载请自行联系原作者
