std.py

NO_STUDENT = int(input('number of student : '))

def write_file(no_student=NO_STUDENT):
    with open('std.txt', 'w') as file :
        for student in range(no_student) :
            fname,lname, age = input(f'student {student+1} : ').split()
            file.writelines(f'{fname} {lname} {age}\n')
            print(f' -- add : {fname} {lname} {age}')
            

def del_select_age(del_age=None):
    print()
    with open('std.txt', 'r') as file :
        students = []
        if not del_age :
            del_age = int(input('\nAge to delete : '))
        
        for student in range(NO_STUDENT) :
            fname,lname, age = file.readline().split()
            if int(age) != del_age :
                students.append(f'{fname} {lname} {age}')
            else :
                print(f' -- delete : {fname} {lname} {age}')

    with open('std.txt', 'w') as file :
        for student in students :
            file.writelines(f'{student}\n')
        

write_file()
del_select_age()