python学习记录三

一、集合：

list_1 = [1,4,5,7,3,6,7,9]
list_1 = set(list_1)

list_2 = set([2,6,0,66,22,8,4])

#交集
list_1.intersection(list_2) #list_1 & list_2

#并集
list_1.union(list_2) #list_1 | list_2

#差集
list_1.difference(list_2) #list_1 - list_2
list_2.difference(list_1) #list_2 - list_1

list_3 = set([1,3,7])
#子集
list_3.issubset(list_1)  #list_3 <= list_1

#父集
list_1.issuperset(list_3) #list_1 >= list_3

#对称差集
list_1.symmetric_difference(list_2) #list_1 ^ list_2

list_4 = set([5,6,8])
list_3.isdisjoint(list_4)  #没有交集返回Ture

list_1.add(999) #添加
list_1.update([888,777,555])

list_1.remove(4) #删除

list_1.discard(‘ddd‘)

len(list_1) #取长

二、文件：

#读
f = open("yesterday","r",encoding="utf-8")
data = f.read()
f.close()

#写
f = open("yesterday2","w",encoding="utf-8")
f.write("我爱北京天安门\n")
f.write("天安门上太阳升")
f.close()

#读前5行
f = open("yesterday","r",encoding="utf-8")
for i in range(5):
    line = f.readline()
f.close()

#读每一行
f = open("yesterday","r",encoding="utf-8")
for index,line in enumerate(f.readlines()):
    if index == 9:
        print(‘---------------------------‘)
        continue
    print(line.strip())

#高效率读
for line in f:
    print(line)
f.close()

f = open("yesterday","r",encoding="utf-8")
print(f.tell())
f.read(5)
print(f.tell()) #打印光标位置
f.seek(0) #光标移到开始位置
f.close()

import sys,time

for i in range(20):
    sys.stdout.write(‘#‘)
    sys.stdout.flush()
    time.sleep(0.2)

三、函数

#递归
def calc(n):
    print(n)
    if int(n/2)>0:
        return calc(int(n/2))
    print("->",n)

calc(10)

#高阶函数
def add (a,b,f):
    return f(a)+f(b)

res = add(3,-6,abs)
print(res)