用python编写一个简单的学生管理系统

好的，下面是一个简单的学生管理系统的 Python 代码：

class Student:
    def __init__(self, name, age, grade):
        self.name = name
        self.age = age
        self.grade = grade

class StudentManagementSystem:
    def __init__(self):
        self.students = []

    def add_student(self, student):
        self.students.append(student)

    def remove_student(self, student):
        self.students.remove(student)

    def get_student_by_name(self, name):
        for student in self.students:
            if student.name == name:
                return student
        return None

    def get_student_by_age(self, age):
        result = []
        for student in self.students:
            if student.age == age:
                result.append(student)
        return result

    def get_student_by_grade(self, grade):
        result = []
        for student in self.students:
            if student.grade == grade:
                result.append(student)
        return result

# 测试代码
s1 = Student('Tom', 18, 10)
s2 = Student('Jerry', 17, 9)
s3 = Student('Alice', 19, 11)

sms = StudentManagementSystem()
sms.add_student(s1)
sms.add_student(s2)
sms.add_student(s3)

print(sms.get_student_by_name('Tom').age)  # 输出：18
print(len(sms.get_student_by_age(18)))     # 输出：1
print(len(sms.get_student_by_grade(10)))   # 输出：1

sms.remove_student(s2)

print(len(sms.students))  # 输出：2

这段代码定义了两个类，`Student` 和 `StudentManagementSystem`。`Student` 类表示一个学生，包含了学生的姓名、年龄和年级。`StudentManagementSystem` 类表示一个学生管理系统，包含了添加、删除和查询学生的功能。在测试代码中，我们创建了三个学生，并添加到学生管理系统中，然后测试了各种查询功能。