使用一个变量all_students保存一个班的学生信息(4个)，每个学生需要保存：姓名、年龄、成绩、电话

# all_students = [
#     {'name': 'stu1', 'age': 19, 'score': 81, 'tel': '192222'},
#     {'name': 'stu2', 'age': 29, 'score': 90, 'tel': '211222'},
#     {'name': 'stu3', 'age': 12, 'score': 67, 'tel': '521114'},
#     {'name': 'stu4', 'age': 30, 'score': 45, 'tel': '900012'},
# ]

1.添加学生：输入学生信息，将输入的学生的信息保存到all_students中
例如输入：姓名: 小明年龄: 20 成绩: 100 电话: 111922 那么就在all_students中添加{'name':'小明', 'age': 20, 'score': 100, 'tel':'111922'}

all_students = [
    {'name': '小花', 'age': 19, 'score': 81, 'tel': '192222'},
    {'name': '小白', 'age': 29, 'score': 90, 'tel': '211222'},
    {'name': '小黑', 'age': 12, 'score': 67, 'tel': '521114'},
    {'name': '小红', 'age': 30, 'score': 45, 'tel': '900012'},
]
student = {}
name = input('请输入学生的姓名：')
student['name'] = name
age = int(input('请输入学生的年龄：'))
student['age'] = age
score = float(input('请输入学生的成绩：'))
student['score'] = score
tel = input('请输入学生的电话')
student['tel'] = tel
all_students.append(student)
print(all_students)

2.按姓名查看学生信息：
例如输入: 姓名: stu1 就打印：'name':'stu1', 'age': 19, 'score':81, 'tel':'192222'

all_students = [
    {'name': '小花', 'age': 19, 'score': 81, 'tel': '192222'},
    {'name': '小白', 'age': 29, 'score': 90, 'tel': '211222'},
    {'name': '小黑', 'age': 12, 'score': 67, 'tel': '521114'},
    {'name': '小红', 'age': 30, 'score': 45, 'tel': '900012'},
]
name_message = input('请输入要查看的学生的姓名：')
for student in all_students:
    if student['name'] == name_message:
        print(student)
        break
else:
    print('该学生不存在')

3.求所有学生的平均成绩和平均年龄

all_students = [
    {'name': '小花', 'age': 19, 'score': 81, 'tel': '192222'},
    {'name': '小白', 'age': 29, 'score': 90, 'tel': '211222'},
    {'name': '小黑', 'age': 12, 'score': 67, 'tel': '521114'},
    {'name': '小红', 'age': 30, 'score': 45, 'tel': '900012'},
]
sum_scores = 0
sum_ages = 0
for student in all_students:
    sum_scores += student['score']
    sum_ages += student['age']
print('所有学生的平均成绩为%.2f' % (sum_scores / len(all_students)))
print('所有学生的平均年龄为%.2f' % (sum_ages / len(all_students)))

4.删除班级中年龄小于18岁的学生

all_students = [
    {'name': '小花', 'age': 19, 'score': 81, 'tel': '192222'},
    {'name': '小白', 'age': 29, 'score': 90, 'tel': '211222'},
    {'name': '小黑', 'age': 12, 'score': 67, 'tel': '521114'},
    {'name': '小红', 'age': 30, 'score': 45, 'tel': '900012'},
]
index = 0
while index < len(all_students):
    if all_students[index]['age'] < 18:
        del all_students[index]
    else:
        index += 1
print(all_students)

5.统计班级中不及格的学生的人数

all_students = [
    {'name': '小花', 'age': 19, 'score': 81, 'tel': '192222'},
    {'name': '小白', 'age': 29, 'score': 90, 'tel': '211222'},
    {'name': '小黑', 'age': 12, 'score': 67, 'tel': '521114'},
    {'name': '小红', 'age': 30, 'score': 45, 'tel': '900012'},
]
count = 0
for index in range(len(all_students)):
    if all_students[index]['score'] < 60:
        count += 1
print('班级中不及格的学生的人数为%d' % count)

6.打印手机号最后一位是2的学生的姓名

all_students = [
    {'name': '小花', 'age': 19, 'score': 81, 'tel': '192222'},
    {'name': '小白', 'age': 29, 'score': 90, 'tel': '211222'},
    {'name': '小黑', 'age': 12, 'score': 67, 'tel': '521114'},
    {'name': '小红', 'age': 30, 'score': 45, 'tel': '900012'},
]
for student in all_students:
    if student['tel'][len(student['tel']) - 1] == '2':
        print(student['name'])