数据Data Abstraction ¶

print('e' in 'Hello')
print(1 in [1,2,3])
print('el' not in 'Hello')
print([1,2] in [1,2,3])

nl=[number**2 for number in range(1,8) if number % 2 == 1]

#数列求和
n=int(input())
sum([1/i if i%2==1 else -1/i for i in range(1,n+1)])

#求 6+66+666+...+666...666
n=int(input())
sum([int('6'*i) for i in range(1,n+1)])

#双变量 -- 看做for的嵌套
[ x*y for x in [1,2,3] for y in [10,20,30] ]

#因数
x = int(input())
[i for i in range(2,x) if x%i==0]

#素数
x = int(input())
not [i for i in range(2,x) if x%i==0]

#zip与推导式组合用法
a = map(int,input().split())
b = map(int,input().split())
[x*y for (x,y) in zip(a,b)]

print(len(r'hello\nworld'))
#在一个字符串字面量前加一个字符r，表示这个字符串是原始字符串，其中的\不被当作是转义字符前缀。

sum([[1,2], [3,4]], [])
Out[13]: [1, 2, 3, 4]

s='Zhejiang'
#切片使用负的下标访问
s[1:-3]--> 'heji'
#切片省略第2个下标，表示从第1个下标开始到最后一个的切片
s[2:] --> 'ejing'
#第1个下标为0时，可以省略
s[:3] --> 'Zhe'
s[:-2] --> 'Zhejia'
#切片使用第3个参数，该参数表示切片选择元素的步长
s[0:5:2] --> 'Zei'
#切片使用第3个参数为负数时，表示逆向取切片，逆向时在下标的右边切
s[-1:0:-1] --> 'gnaijeh'
s[::-1] --> 'gnaijehZ'

s = input()
##下标写法
while i < len(s):
	print(s[i])
	i+=1
    
##for in写法
for i in s:
	print(i)
    
##enumerate()写法
for i, element in enumerate(seq):
    print(i, element)
    
##内置函数iter()
for every_char in iter(girl_str):
 print(every_char)

## 字符串切片
a[::-1]
## reversed函数
print(''.join(reversed(a)))
## 利用列表

a, b = map(int, input().split('/'))

'12/18'.split('/')` --> `['12', '18']

from matplotlib_venn import venn3
import matplotlib.pyplot as plt

set1 = {1,2,3} ## 等同于 set1=set((1,2,3))
set2 = {2,3,4}
set3 = {3,4,5}
# Use the venn3 function
venn3([set1,set2,set3],  ('set1', 'set2','set3'))
plt.show()

##挑选名单
#要在104位同学中随机挑选20位参加周三上午的连麦分享，但是有7位同学已经在预定的名单中了
#输⼊数据：104⼈名单（学号）和7⼈名单（学号）
#输出数据：20⼈名单和剩下的84⼈名单
import random
ta = {'3190101849', '3190102191', '3190104143', '3190104515'
, '3190104602', '3190104958', '3190105360'}
md = set()
for i in range(104): 
    md.add(input())
md -= ta
tc = set(random.sample(md, 13))  # 随机取样
tc = tc | ta
print(*tc, sep='\n') 
print('-'*80)
print(*(md-tc), sep=', ')

fac={'math': '0001', 'python': '0002', 'c': '0003'}
print(fac)

fac=dict([("math","0001"),("python","0002"),("c","0003")])
print(fac)

fac=dict(math="0001",python="0002",c="0003")
print(fac)

#json将字符串转换为字典
import json
user_info= '{"name" : "john", "gender" : "male", "age": 28}'
user_dict = json.loads(user_info)

###用items()实现字典遍历
score = {'张三':78, '李四':92, '王五':89}
for key,value in score.items():
    print(f'{key}:{value}')

##星期
days={1:"Mon",2:"Tue",3:"Wed",4:"Thu",5:"Fri",6:"Sat",7:"Sun"}
num=int(input())
print(days[num])

##四则运算
result={
    "+":"x+y",
    "-":"x-y",
    "*":"x*y",
    "/":'x/y if y!=0 else "divided by zero"'}
r=eval(result.get(z)) 

##统计各位数字次数
str=input() 
countchar={}
for c in str: 
    countchar[c]=countchar.get(c,0)+1
print(countchar)

## sort by key
cnt = sorted(cnt.items(), key=lambda d: d[0], reverse=False)

## sort by value
cnt = sorted(cnt.items(), key=lambda d: d[1], reverse=False)

可以根据两个乘数，查阅字典得到乘积。以3的乘法为例：
d1={(3,1):3,(3,2):6,(3,3):9,(3,4):12,(3,5):15,(3,6):18,(3,7):21,(3,8):24, (3,9):27}
d1[(3,9)]

r = range(1,10)
s = iter(r)
next(s)

# 列表
for item in [1, 2, 3]:
    print(item)

# 字符串
for char in "hello":
    print(char)

d = {'a': 1, 'b': 2}

# 键迭代
for key in d:
    print(key)

# 值迭代
for value in d.values():
    print(value)

# 键值对迭代
for k, v in d.items():
    print(k, v)

with open('data.txt') as f:
    for line in f:  # 文件对象本身就是行迭代器
        print(line.strip())

for index, value in enumerate(['a', 'b', 'c']):
    print(index, value)
# 输出:
# 0 a
# 1 b
# 2 c

names = ['Alice', 'Bob']
ages = [25, 30]
for name, age in zip(names, ages):
    print(name, age)
# 输出:
# Alice 25
# Bob 30

# 惰性计算
squares = map(lambda x: x**2, [1, 2, 3])
print(list(squares))  # [1, 4, 9]

evens = filter(lambda x: x % 2 == 0, [1, 2, 3, 4])
print(list(evens))  # [2, 4]

for i in reversed(range(5)):
    print(i)  # 4, 3, 2, 1, 0

from itertools import count
my_list =["Geeks", "for", "Geeks"]
  
for i in zip(count(start = 1, step = 1), my_list):      
    print(i)

ranks = ['A', 'K', 'Q', 'J', '10', '9', '8', '7', '6', '5', '4', '3', '2'
         suits = ['H', 'D', 'C', 'S']
# 生成器表达式版本
cards = ((suit, rank) for suit in suits for rank in ranks)
print(*cards)

# product版本
import itertools as it
cards = it.product(suits, ranks)
print(*cards)

def simple_generator():
    print("开始")
    yield 1
    print("继续")
    yield 2
    print("结束")

gen = simple_generator()  # 创建生成器对象(不执行函数体)
print(next(gen))  # 输出"开始"，然后返回1
print(next(gen))  # 输出"继续"，然后返回2
print(next(gen))  # 输出"结束"，然后抛出StopIteration

#把⽣成器表达式⽤作函数的参数值时，外⾯的圆括号可以省略
sum(x*x for x in range(10))
#但是当生成器表达式只是函数的参数之一时，必须有外面的圆括号
def fun(f, b):
    for x in b:
        f(x)

fun(print, x for x in range(10)) # Error

def countdown(n):
    while n > 0:
        yield n
        n -= 1

# 调用生成器函数
generator = countdown(5)

print(next(generator))  # 输出：5
print(next(generator))  # 输出：4
print(next(generator))  # 输出：3
print(next(generator))  # 输出：2
print(next(generator))  # 输出：1

def read_large_file(file_path):
    with open(file_path) as f:
        for line in f:
            yield line.strip()

# 逐行处理，不一次性加载整个文件
for line in read_large_file("huge_file.txt"):
    process(line)

def infinite_sequence():
    num = 0
    while True:
        yield num
        num += 1

for i in infinite_sequence():
    if i > 100:
        break
    print(i)

def pipeline(data):
    # 第一阶段处理
    processed = (x.upper() for x in data if x.strip())
    # 第二阶段处理
    filtered = (x for x in processed if not x.startswith("A"))
    yield from filtered  # Python 3.3+语法

data = ["apple", " banana", "orange", " pear"]
print(list(pipeline(data)))  # [' BANANA', 'ORANGE', ' PEAR']