学习笔记(四)集合、文件与函数

1.集合也是无序的

list_1=[1,4,5,7,3,6,7,9]
list_2=set([2,6,0,66,22,8,4])
list_1.intersection(list_2)#交集  list_1 & list_2
list_1.union(list_2)#并集  list_1 | list_2
list_1.symmetric_difference(list_2)#对称差集    list_1 ^ list_2
list_1.difference(list_2)#差集    list_1 - list_2
list_1.issubset(list_2)#父集
list_1.issubset(list_2)#子集

2.文件

  操作流程
    1.打开文件，获取句柄
        file=open("文件名",encoding="UTF-8")
        with open("文件名","r",encoding="UTF-8") as file:
    2.通过句柄对文件进行操作
        file.read()#默认读所有
        file.write()
        file.close()

        file.readline()
        '''readline([size]) -> next line from the file, as a string.
        Retain newline.  A non-negative size argument limits the maximum
        number of bytes to return (an incomplete line may be returned then).
        Return an empty string at EOF.'''
        for i in file:#一行一行的读入
            print(i)

        file.readlines()#list of strings, each a line from the file.
        for index,value in enumerate(file.readline()):#一次性读入文件
        #enumerate(iterable[, start]) -> iterator for index, value of iterable
            print (index)

        file.tell()#int值 Current file position  按字符长度

        file.seek()#file.seek()# Move to new file position.

        file.flush()#Flush the write buffers of the stream if applicable.

        file.truncate()#Truncate the file to at most size bytes from the current file position
    3.关闭文件
    file.close()

3.函数

def test(*args):#以元组参数,给函数传递不固定参数
        print (args)
    test(1,2,3,4,5)

    def test1(*args):#以元组参数,给函数传递不固定参数
        print (args)
    test1(*[1,2,3,4,5])


    def test2(**args):#将关键字参数以字典形式
        print (args)
    test2(name='111',age=222)
    test2(**{'name':'111','age':222} )

    #高阶函数---将函数本身当做参数传递给另一个函数
    def add(a,b,f):
        return f(a)+f(b)
    print (add(3,-6,abs))

4.字节码

   str="你好"
    str1=str.decode("gbk")
    print(str1)
    print(sys.getdefaultencoding())

    for i in range(50):
    sys.stdout.write("■")
    sys.stdout.flush()
    time.sleep(0.1)