How to get object from class based on unique attribute?

I have a class called Student, where they have two attributes: studentName and a unique number for each student, studentID.

In another class, called Course, I already have a function
add_student(self, student) that adds the given student to the given course. I want to create another function add_student_list(self, lst) which intakes a list of studentIDs. I have a for loop which looks at the IDs in lst to see which students to add, I just need to call the add_student(self, student) function for the ones in lst, however, I’m unable to do this, as I only have an id, and not the student object.

So my question is, how can I call the necessary student object based on the unique ID?

EDIT: here’s the relevant part for my code:

import itertools
import pandas as pd

class Student (object):
    #The following two objects are used to assign them unique IDs and to keep track of them.
    id_iter = itertools.count()
    all_students = pd.DataFrame(columns=["Student", "Student ID"])
    
    #Adding a new student:
    def __init__(self, studentName):
        #The name of the student will be given, the ID will be generated:
        self.studentName = [studentName, next(self.id_iter)]
        #The new student will have a list of courses attended:
        self.courses = pd.DataFrame(columns=["Course", "Course ID", "Passed/Failed", "Completed Assignments"])
        #The new student will be added to the list of all students:
        Student.all_students = pd.concat([Student.all_students, pd.DataFrame.from_dict({"Student": self.studentName[0], "Student ID": self.studentName[1]}, orient = "index")], ignore_index = True, axis = 1)
        Student.all_students = Student.all_students.dropna(axis=1)
    
    def __str__(self):
        return str(self.studentName)

class Course (object):
    #The two objects are similar to that of the student class:
    id_iter = itertools.count()
    all_courses = pd.DataFrame(columns=["Course", "Course ID"])
    
    #the courses are similarly added as students above

    def add_student(self,student,completed_assignments):
    #this adds students with the number of assingments they completed (not relevant), the code is not relevant

    def add_student_list(self, lst):
        for i in range(0,len(lst)):
            for j in range(0,len(Student.all_students.swapaxes("index", "columns"))):
                if lst[i][0] == Student.all_students[j][1]:
                    self.add_student()

>Solution :

Two methods:

1. Store your students in a dictionary with a id as the key. Than can retrieve the students based on their ids.

2. Search through the students everytime you have a list.

ids_to_search = [2, 34, 3]
students = [student for student in students if student.id==id_to_search]