Student Management System

import json
import os

class Student:
    def __init__(self, roll_no, name, marks):
        self.roll_no = roll_no
        self.name = name
        self.marks = marks  # dict: {"Math": 85, "Python": 92}

    @property
    def average(self):
        return sum(self.marks.values()) / len(self.marks) if self.marks else 0

    @property
    def grade(self):
        avg = self.average
        if avg >= 90: return "A+"
        elif avg >= 80: return "A"
        elif avg >= 70: return "B"
        elif avg >= 60: return "C"
        elif avg >= 50: return "D"
        return "F"

    def to_dict(self):
        return {"roll_no": self.roll_no, "name": self.name, "marks": self.marks}

    def __str__(self):
        return f"Roll: {self.roll_no} | {self.name} | Avg: {self.average:.1f} | Grade: {self.grade}"

class StudentManager:
    def __init__(self, filename="students.json"):
        self.filename = filename
        self.students = self._load()

    def _load(self):
        if os.path.exists(self.filename):
            with open(self.filename) as f:
                data = json.load(f)
                return [Student(**s) for s in data]
        return []

    def _save(self):
        with open(self.filename, "w") as f:
            json.dump([s.to_dict() for s in self.students], f, indent=2)

    def add_student(self):
        roll = input("Roll Number: ")
        if any(s.roll_no == roll for s in self.students):
            print("Roll number already exists!")
            return
        name = input("Name: ")
        subjects = input("Subjects (comma-separated): ").split(",")
        marks = {}
        for sub in subjects:
            sub = sub.strip()
            marks[sub] = float(input(f"  Marks in {sub}: "))
        self.students.append(Student(roll, name, marks))
        self._save()
        print(f"✅ Student '{name}' added!")

    def view_all(self):
        if not self.students:
            print("No students found!")
            return
        print("\n--- All Students ---")
        for s in self.students:
            print(f"  {s}")

    def search(self):
        query = input("Search by name or roll: ").lower()
        results = [s for s in self.students if query in s.name.lower() or query == s.roll_no.lower()]
        if results:
            for s in results:
                print(s)
        else:
            print("No students found!")

    def delete(self):
        roll = input("Roll number to delete: ")
        self.students = [s for s in self.students if s.roll_no != roll]
        self._save()
        print("Student deleted!")

def main():
    mgr = StudentManager()
    while True:
        print("\n1.Add 2.View All 3.Search 4.Delete 5.Exit")
        ch = input("Choice: ")
        if ch == "1": mgr.add_student()
        elif ch == "2": mgr.view_all()
        elif ch == "3": mgr.search()
        elif ch == "4": mgr.delete()
        elif ch == "5": break

main()