如何在列表，字典，集合中根据条件筛选数据

过滤掉列表中的负数

from random import randint
data = [randint(-10, 10) for _ in xrange(10)] # 创建10个-10到+10的随机数 3 xrange->range

print(data)

data1 = filter(lambda x: x>=0, data)

print(data)
print(data1)

$ python learning.py
[7, -10, 5, 2, -10, 6, -4, -2, 1, -6]
[7, -10, 5, 2, -10, 6, -4, -2, 1, -6]
[7, 5, 2, 6, 1]

data1 = [x for x in data if x >= 0]

print(data)
print(data1)

timeit 列表解析更快都远快于跌代方案

# 迭代
res = []
for x in data:
    if x >= 0:
        res.append(x)
print res

d = {x: randint(60, 100) for x in xrange(1,21)}
print d
c = {k: v for k, v in d.iteritems() if v > 90}
print c

筛出集合中能被3整除的元素

data = [randint(-10, 10) for _ in xrange(10)] #xrange->range

s = set(data)

r = {x for x in s if x%3 == 0}

print r

如何为元组中的每个元素命名，提升程序可读性？

// C
#define NAME 0
#define AGE 1
enum Student {
    NAME,
    AGE,
    SEX,
}

# ('jim', 16, 'male', 'jim872@mail.com')
# ('liLei', 17, 'male', 'leile@qq.com')
# ('Lucy' 16, 'female', 'lucy123@yahoo.com')

# NAME = 0
# AGE = 1
# SEX = 2
# EMAIL = 3
NAME, AGE, SEX, EMAIL = xrange(4)

student = ('jim', 16, 'male', 'jim872@mail.com')

# name
print student[NAME]

# age

if student[AGE] >= 18:
    # ...

# sex
if student[SEX] == 'male':
    # ...

# 开销比普通元组大一点点
from collections import namedtuple

Student = namedtuple('Student', ['name', 'age', 'sex', 'email'])

s = Student('jim', 16, 'male', 'jim872@mail.com')

# name
print s.name

# age
print s.age

# sex
print s.sex

r = isinstance(s, tuple)
print r  # True

如何统计序列中元素的出现频度

某随机序列中，找到出现次数最高的3个元素，他们出现次数是多少？

from random import randint

data = [randint(0, 20) for _ in xrange(30)]

print data

c = dict.fromkeys(data, 0)
print c

for x in data:
    c[x] += 1
print c

from random import randint

data = [randint(0, 20) for _ in xrange(30)]

print data

from collections import Counter

c2 = Counter(data)

print c2

c3 = c2.most_common(3)
print c3

对某英文文章的单词，进行词频统计，找到出现次数最高的10个单词，他们出现次数是多少？

import re
from collections import Counter
txt = open('aaa.txt').read()
print txt

c = re.split('\W+',txt)
print c
c1 = Counter(c)
print c1
c2 = c1.most_common(1)
print c2

如何根据字典值的大小，对字典中的项排序

某班英语成绩以字典形式存储为，根据成绩高低，计算学生排名.

sorted([9, 1, 2, 8, 5])

# 存储空间少一些浪费 itervalues(), iterkeys()
from random import randint
c = {x: randint(60, 100) for x in 'xyzabc'}
print c
c1 = sorted(c)
print c1

c2 = iter(c)
print c2

c3 = list(iter(c))
print c3

c4 = (97, 'a') > (69, 'b')
print c4

c5 = (97, 'b') > (97, 'a')
print c5

c6 = (97, 'a') > (97, 'b')
print c6

c7 = c.keys()
print c7

c8 = c.values()
print c8

c9 = zip(c8, c7)
print c9


c10 = zip(c.itervalues(), c.iterkeys())
print c10

c11 = sorted(c10)
print c11

c12 = c.items()
print c12
c13 = sorted(c.items(), key=lambda x: x[1])
print c13

如何快速找到多个字典中的公共键（key）

西班牙⚽️联赛，每轮球员进球统计，统计出前N轮，每场比赛都有进球的球员

$ s1.view
$ s1.viewkeys?

from random import randint,sample

a = sample('abcdefg', 3)
print a

b = sample('abcdefg', randint(3,6))
print b

s1 = {x:randint(1, 4) for x in sample('abcdefg', randint(3, 6))}
print s1
s2 = {x:randint(1, 4) for x in sample('abcdefg', randint(3, 6))}
s3 = {x:randint(1, 4) for x in sample('abcdefg', randint(3, 6))}

res = []

for k in s1:
    if k in s2 and k in s3:
        res.append(k)
print res

c = s1.viewkeys()
print c

r = s1.viewkeys() & s2.viewkeys() & s3.viewkeys()
print r

r1 = map(dict.viewkeys, [s1, s2, s3])
print r1

r2 = reduce(lambda a,b: a&b, r1)
print r2

如何让字典保持有序

某编程竞赛系统，对参赛选手编程解题进行计时，选手完成题目后，把该选手解题用时记录到字典中，以便选手查询成绩，（答题用时越短越优），比赛结束后，需按排名顺序打印选手成绩，如何实现

d = {}

d['Jim'] = (1, 35)
d['leo'] = (2, 37)
d['Bob'] = (3, 40)

for k in d:
    print k

from collections import OrderedDict

d1 = OrderedDict()
d1['Jim'] = (1, 35)
d1['leo'] = (2, 37)
d1['Bob'] = (3, 40)
for k in d1:print k

from time import time
from random import randint
from collections import OrderedDict

d = OrderedDict()
players = list('ABCDEFGH')
print players
start = time()

for i in xrange(8):
    raw_input()
    p = players.pop(randint(0, 7-i))
    end = time()
    print i + 1, p, end - start
    d[p] =(i+1, end-start)

print
print '-' * 20

for k in d:
    print k,d[k]

如何实现用户的历史记录功能（最多n条）

制作一个简单的小游戏，添加历史记录功能，显示用户最近才过的数字，如何实现？

from collections import deque

q = deque([], 5)
c = q.append(1)
print q

q.append(2)
q.append(3)
q.append(4)
q.append(5)
print q

q.append(6)
print q

from random import randint
from collections import deque

N = randint(0, 100)
history = deque([],5)
def guess(k):
    if k == N:
        print 'right'
        return True
    if k < N:
        print '%s is less than N' % k
    if k > N:
        print '%s is greater than N' % k

while True:
    line = raw_input("please input a number:")
    if line.isdigit():
        k = int(line)
        history.append(k)
        if guess(k):
            break
    elif line == 'history' or line == 'h?':
        print list(history)

$ pickle.dump?
$ pickle.load?

from collections import deque
import pickle

q = deque([], 5)
c = q.append(1)

q.append(2)
q.append(3)
q.append(4)
q.append(5)

pickle.dump(q, open('history', 'w'))

q2 = pickle.load(open('history'))
print q2