open（）函数 '''文件处理open函数的用法：读、写、追加模式 文件处理写 f = open("1.py","w",encoding="utf-8") data = f.write("111\n") f.close() 文件处理读 r = open("1.py","r",encoding="utf-8") data = r.read() print(data) r.close() 文件处理追加 a = open("1.py","a",encoding="utf-8") data = a.write("2222\n") a.close() with的用法：可以省略掉python不释放内存的问题 文件处理读 with open("1.py","r",encoding="utf-8") as r: print(r.read()) 文件处理写 with open("1.py","w",encoding="utf-8") as w: w.write("3333\n") 文件处理追加 with open("1.py","a",encoding="utf-8") as a: a.write("4444\n") 将源文件写入新的文件中 with open("1.py","r",encoding="utf-8") as r ,open("2.py","w",encoding="utf-8") as w: w.write(r.read()) 追加文件到源文件中 with open("1.py","r",encoding="utf-8") as r ,open("1.py","a",encoding="utf-8") as a: a.write("11111\n") data = r.read() print(data) b模式 b模式的读、写、追加 文件读模式 f = open("1.py","rb")#b模式不需要指定编码格式 data = f.read() print(data) #查看到是bytes格式 print(data.decode("utf-8")) #解码 转换模式： 字符串----------encode-----------bytes bytes-----------decode-----------字符串 文件写模式 f = open("1.py","wb") f.write(bytes("22222\n",encoding="utf-8")) f.write(bytes("张三\n",encoding="utf-8")) #编码方法1 f.write("李四".encode("utf-8")) #编码方法2 文件追加模式 a = open("1.py","ab") a.write(bytes("张三\n",encoding="utf-8")) a.write("李四\n".encode("utf-8")) '''

# 其他方法: # f = open("1.py","r",encoding="utf-8",newline="")   #读取文件中真正的换行符合 # print(f.readlines()) # print(f.tell())   #光标位置 # f.seek(3)    #指定光标所在位置（以字节为单位） # f.read(3) #代表读取3个字符 # f.truncate() #文件截断，以r+、a+模式打开，w+模式不可以，会清空文件

# 文件操作倒着查找： # f = open ("日志文件","rb") # 方式一： # data = f.readlines() # print(data[-1].decode("utf-8"))    #切片方式，截取最后一段 # 方式二： # for i in f.readlines(): #for循环以列表形式一行一行读取打开的文件 # print(i) # for i in f: # offs = -10 #定义一个倒序变量 # while True: # f.seek(offs,2) #以2倒序模式读取10个字节 # data = f.readlines() #一行一行读取打开的文件，组成列表 # if len(data) > 1: #判断读取的行数是否大于1，如果小于1，则offs*=2增加一倍读取 # print("文件的最后一行是%s" %(data[-1].decode("utf-8"))) # break # offs *=2 #读取行数小于一行，说明字节数不够，增加一倍，倒数20个字节

#三元表达式 # name = "alex" # name = "tom" # res="low货" if name == "alex" else "帅锅" # print(res) #列表解析 还可以结合三元表达式，结合判断； # 常规方法一 # egg_list = [] # for i in range(10): # egg_list.append("蛋%s" %i) # print(egg_list) #列表解析方法二 # l = ["蛋%s" %i for i in range(10)] # print(l) # 生成器表达式 省内存 # l_m = ("鸡蛋%s" %i for i in range(10)) # # 每次生成一个，next方法 # # 方法一 # print(l_m.__next__()) # # 方法二 # print(next(l_m)) #next本质就是调用__next__

生成器函数：yield

1 import time 2 def test(): 3     print('开始打印') 4     yield 1 5     time.sleep(3) 6     yield 2 7     time.sleep(3) 8     yield 3 9 res = test()10 print(res)11 print(res.__next__())   #nest方式12 print(next(res))13 print(next(res))

 人口普查py

1 #人口表2 {
   'name':'北京','population':10}3 {
   'name':'山东','population':20}4 {
   'name':'山西','population':30}5 {
   'name':'西安','population':40}6 {
   'name':'河北','population':50}

1 #人口统计和百分比 2 #函数 3 def get_population(): 4     with open("人口","r",encoding="utf-8") as f:   #打开一张表，相对路径 5         for i in f : 6             yield i 7 g = get_population()   #函数执行第一次 8 g1 = get_population()  #函数执行第二系 9 #调用第一次执行，求出总人数10 all_pop = sum(eval(i)["population"] for i in g)11 print("总人口%s" % all_pop)12 #调用第二次函数执行，求出每个省对应人数13 s1 = g1.__next__()14 print("%s"'%.2f %%' % (eval(s1)["name"] ,eval(s1)["population"] / all_pop))15 s2 = g1.__next__()16 print('%s''%.2f %%' % (eval(s2)["name"] ,eval(s2)["population"] / all_pop))17 s3 = g1.__next__()18 print('%s''%.2f %%' % (eval(s3)["name"] ,eval(s3)["population"] / all_pop))19 s4 = g1.__next__()20 print('%s''%.2f %%' % (eval(s4)["name"] ,eval(s4)["population"] / all_pop))21 s5 = g1.__next__()22 print('%s''%.2f %%' % (eval(s5)["name"] ,eval(s5)["population"] / all_pop))