To include the functionality you described, you'll need to implement a new window that allows you to select student data with radio buttons for marking attendance and then record the attendance in a separate Excel file.

This new functionality will include the following steps:

1. Create a new window when the 'Mark Attendance' button is pressed.
2. Load student data from a CSV file and display it in a list with radio buttons for present or absent.
3. Collect the attendance data and save it to a new Excel file; also calculate the count of present and absent students.

Here is the Python code to achieve the functionality, with explanations on where to add it to your existing program:

Step 1: Define a new function to handle the mark attendance process. You need to add this function definition below the choose_file_and_update() function in your existing code:

import openpyxl  # Make sure to install this package

# Function to load students, mark attendance, and save the results
def mark_attendance():
    attendance_window = tk.Toplevel()  # Create a new top-level window
    attendance_window.geometry("600x400")
    attendance_window.title("Mark Student Attendance")

    def save_attendance():
        # Save the attendance to an Excel file
        wb = openpyxl.Workbook()
        sheet = wb.active
        sheet.title = 'Attendance'
        sheet.append(["Student Name", "Roll Number", "Attendance"])
        
        present_count = 0
        absent_count = 0
        for entry in attendance_data:
            attendance = 'Present' if entry['attendance'].get() == 'P' else 'Absent'
            sheet.append([entry['name'], entry['roll_number'], attendance])
            if attendance == 'Present':
                present_count += 1
            else:
                absent_count += 1
                
        # Add the counts to the end of the Excel file
        sheet.append([])
        sheet.append(['Total Present', present_count])
        sheet.append(['Total Absent', absent_count])
        
        save_path = filedialog.asksaveasfilename(defaultextension=".xlsx", filetypes=[("Excel files", "*.xlsx")])
        if save_path:
            wb.save(save_path)
            tkmb.showinfo("Success", "Attendance saved successfully")
    
    # Function to load students data into the window
    def load_students():
        filepath = filedialog.askopenfilename(filetypes=[("CSV files", "*.csv")])
        if filepath:
            with open(filepath, newline='') as csvfile:
                reader = csv.DictReader(csvfile)
                for i, row in enumerate(reader, 1):
                    row_frame = tk.Frame(attendance_window)
                    row_frame.pack(fill='x')
                    tk.Label(row_frame, text=row['Student Name']).pack(side='left')
                    tk.Label(row_frame, text=row['Roll Number']).pack(side='left', padx=(10, 0))
                    
                    attendance_var = tk.StringVar(value='A')  # Default to absent
                    
                    present_rb = tk.Radiobutton(row_frame, text='Present', variable=attendance_var, value='P')
                    present_rb.pack(side='left', padx=(10, 0))
                    
                    absent_rb = tk.Radiobutton(row_frame, text='Absent', variable=attendance_var, value='A')
                    absent_rb.pack(side='left', padx=(10, 0))
                    
                    attendance_data.append({'name': row['Student Name'], 'roll_number': row['Roll Number'], 'attendance': attendance_var})
    
    attendance_data = []  # Hold the attendance data as a list of dicts
    
    load_button = ctk.CTkButton(attendance_window, text='Load Students', command=load_students)
    load_button.pack(pady=12)
    
    save_button = ctk.CTkButton(attendance_window, text='Save Attendance', command=save_attendance)
    save_button.pack(pady=12)

    attendance_window.mainloop()

Step 2: Modify the 'Mark Attendance' button command. Locate the 'Mark Attendance' tab section in your code and change the register_button1 command option to command=mark_attendance:

register_button1 = ctk.CTkButton(master=mark_attendance_frame, text='Mark Attendance', command=mark_attendance)
register_button1.pack(pady=12, padx=10)

Now, when you run your application and go to the 'Mark Attendance' tab, you should be able to load the student data from a CSV file and mark each student's attendance as present or absent.

Also note, you will need to install openpyxl if it's not already installed, as it's required to create Excel files:

pip install openpyxl

Keep in mind that attendance_data stores the necessary information within the mark_attendance function and allows you to save the data to an Excel file with a summary of attendance at the end.