def main():
  sum =0.0
  count =0
  moredata ='yes'  #字符串
  while moredata[0] =='y': #获取字符串第一个字符，true执行下面的
    x =eval(input('enter a number'))
    sum =sum+x
    count = count +1
    moredata =input("你有更多的number(yes or no)")
  print("pingjunshushi:\n",sum/count)
main()
enter a number 3
你有更多的number(yesor no)y
enter a number 4
你有更多的number(yesor no)n
pingjunshushi:
 3.5

def main():
  sum =0
  count =0
  xStr = input("enter a number")
  while xStr != "":  #空字符串
    x = eval(xStr)  #转换字符串为数字的过成
    sum = sum + x
    count =count +1
    xStr = input("enter a number :")
  print("average is",sum/count)
main()
enter a number6
enter a number :6
enter a number :6
enter a number :  这里确认输入不是哨兵空字符才将输入字符串转换为数字
average is 6.0

def main():
  fileName = input("file denumber:") #这个相当于一个文件
  infile = open(fileName,'r') #open(文件名，方式'r'/'w')函数用来打开这个文件的一行保存在infile列表（相当一个数组）中
  sum =0
  count = 0
  for line ininfile:   #循环变量line遍历文件的每一行（文件每一行已经保存在infile列表中），将每一行执行下面的代码
    sum = sum+eval(line)
    count = count +1
  print("aveage is:",sum/count)
main()

line=infile.readline()
while line != "":
#处理每一行
line =infile.readline()

while True:
  try:
    x = int(input("输入一个数字："))
    break
  except ValueError:
    print("重新输入：")

dict1={"name":"liyue"}
dict2=dict1.copy()
print("dict2 is:",str(dict2))