Python 编程问题？

~ age = {'小红': 18, '小刚': 20, '小明': 19, '小丽': 18, '小文': 17}

age['小伟'] = 17 #向字典中添加 '小伟': 17
print(age)

age['小刚'] = 21 #将小刚年龄修改为21
print(age)

del age['小丽'] #删除小丽年龄对应的键值对
print(age)

sum = 0.0 #定义一个变量sum 为累加和
count = 0 #定义一个变量 count 为数量
for value in age.values(): #循环遍历所有的age
sum += value #累加和
count += 1 #累加数量

print('这几个学生的平均年龄为：','{}'.format(sum/count)) #输出平均年龄

#!/usr/bin/env python
age={'小红': 18, '小刚':20, '小明': 19, '小丽': 18, '小文': 17}
print(age)
age['小伟']=17
print(age)
age['小刚']=21
print(age)
del age['小丽']
print(age)
total = 0.0
count = 0
for name in age:
total += age[name]
count += 1

print("{:.1f}".format(total/count))