１.如何在列表, 字典, 集合中根据条件筛选数据¶
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from random import randint
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data = [randint(-10,10) for _ in range(10)]
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data
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# 筛选出列表中大于０的元素
# 使用filter函数
list(filter(lambda x:x>=0,data))
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# 列表解析
[x for x in data if x >= 0]
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timeit list(filter(lambda x:x>=0,data))
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timeit [x for x in data if x >= 0]
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# 字典解析
d = {x:randint(60,100) for x in range(1,21)}
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d
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{k:v for k,v in d.items() if v > 90 }
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# 集合解析
s = set(data)
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s
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{x for x in s if x % 2 == 0}
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2.如何为元组中的每个元素命名, 提高程序可读性¶
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#方案一,定义一系列数值常量
NAME,AGE,SEX,EMAIL = range(4)
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student = ('Tom','16','male','tom@gmail.com')
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student[NAME]
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#方案二，使用namedtuple
from collections import namedtuple
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Student = namedtuple('Student',['name','age','sex','email'])
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#位置传参
s = Student('Tom','16','male','tom@gmail.com')
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s
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#关键字传参
s2 = Student(name='Tom',age='16',sex='male',email='tom@gmail.com')
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s2
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s.name
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s.email
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isinstance(s,tuple)
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3.如何统计序列中元素的出现频度¶
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from random import randint
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data = [randint(0,20) for _ in range(30)]
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data
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#fromkeys：用于创建并返回一个新的字典。两个参数：第一个是字典的键，第二个（可选）是传入键的值，默认为None。
c = dict.fromkeys(data,0)
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c
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for x in data:
c[x] += 1
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c
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# 使用Counter
from collections import Counter
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c2 = Counter(data)
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c2
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#找出频率出现最高的３个元素
c2.most_common(3)
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import re
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txt = open('Alice.txt').read()
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c3 = Counter(re.split('\W+',txt))
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c3
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c3.most_common(10)
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4.如何根据字典中值的大小, 对字典中的项排序¶
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sorted([9,3,1,67,6])
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from random import randint
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d = {x:randint(60,100) for x in 'xyzabc'}
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d
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d.keys()
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d.values()
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#方案一：利用zip将字典转换成元组进行排序
sorted(zip(d.values(),d.keys()))
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d.items()
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#方案二：传递sorted函数的key参数
sorted(d.items(),key=lambda x:x[1])
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5.如何快速找到多个字典中的公共键(key)¶
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from random import randint,sample
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from random import randint,sample
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# 取样
sample('abcdef',3)
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sample('abcdef',randint(3,6))
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# 找出s1,s2,s3中都存在的key
# 方案一:遍历
s1 = {x:randint(1,4) for x in sample('abcdef',randint(3,6))}
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s1
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s2 = {x:randint(1,4) for x in sample('abcdef',randint(3,6))}
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s3 = {x:randint(1,4) for x in sample('abcdef',randint(3,6))}
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s2
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s3
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res = []
for k in s1:
if k in s2 and k in s3:
res.append(k)
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res
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# 方案二：使用集合
s1
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s1.keys()
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s2.keys()
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s1.keys() & s2.keys() & s3.keys()
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# 方案三：使用map和reduce
# Python3里，map返回的结果是迭代器(iterator)
list(map(dict.keys,[s1,s2,s3]))
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from functools import reduce
# reduce() 函数会对参数序列中元素进行累积。
reduce(lambda a,b:a & b,map(dict.keys,[s1,s2,s3]))
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6.如何让字典保持有序¶
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d = {}
d['Tom'] = (1,35)
d['Bob'] = (2,37)
d['Kate'] = (3,45)
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d
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# python3.6之后字典有序,按照数据存入的顺序
for k in d:
print(k)
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# 有序字典OrderedDict
from collections import OrderedDict
d = OrderedDict()
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d['Tom'] = (1,35)
d['Bob'] = (2,37)
d['Kate'] = (3,45)
for k in d:
print(k)
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from time import time
from random import randint
from collections import OrderedDict
d = OrderedDict()
players =list('ABCDEFGH')
start = time()
for i in range(8):
'''模拟选手比赛消耗时间并存入字典中'''
input()
p = players.pop(randint(0,7-i))
end = time()
print(i + 1, p, end - start,sep=' ')
d[p] = (i + 1, end - start)
print('-' * 30)
for k in d:
print(k, d[k])
7.如何实现用户的历史记录功能(最多n条)¶
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from collections import deque
# 创建双向队列
q = deque([], 5)
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q
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q.append(1)
q.append(2)
q.append(3)
q.append(4)
q.append(5)
q
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q.append(6)
q
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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)
else:
print('%s is greater-than N' % k)
return False
while True:
line = 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))
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import pickle
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q
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# 将数据存入文件
pickle.dump(q,open('history','wb'))
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# 读取文件
q2 = pickle.load(open('history','rb'))
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q2
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