space invader with dsa attempt

import turtle
import os
import math
import random

list = []
c_id = 0
mlst = []

def adduser():
    global c_id
    print("\n----- Add User -----")
    idn = len(list) + 1
    firstn = input("First name: ")
    lastn = input("Last name: ")
    ema = input("Email: ")
    search = bsearch(mlst, ema)
    if search == 1:
        print("\n!!! Email has already been used. Try again!!!\n")
        main()
    else:
        c_id+=1
        passw = input("Password: ")
        print(">>> Student added with ID: {}".format(c_id))
    user = {
        "ID" : idn,
        "Firstname" : firstn,
        "Lastname" : lastn,
        "Mail" : ema,
        "Password" : passw}

    mlst.append(ema)
    mailsort(mlst, "Mail")
    list.append(user)
    wait()
    main()

def dispuser():
    global list
    dictsort(list, "ID")
    print("\n----- Display Users -----")
    print("ID\t\t\t", "Name\t\t\t\t", "Email")
    for i in range(len(list)):
        name = str(list[i]["Firstname"] + " " + list[i]["Lastname"])
        ID = str(list[i]["ID"])
        mail = str(list[i]["Mail"])

        print(ID,"\t\t\t",name,"\t\t\t",mail)

def bsearch(mlst, maill):
    first = 0
    last = len(mlst)-1
    found = 0
    while first <= last and not found:
        midpoint = (first + last)//2
        if mlst[midpoint] == maill:
            found = 1
        else:
            if maill < mlst[midpoint]:
                last = midpoint - 1
            else:
                first = midpoint + 1
    return found

def mailsort(mlst, maill):
    for fillslot in range(len(mlst) -1, 0 , -1):
        positionOfMax = 0
        for location in range(1, fillslot + 1):
            if mlst[location] > mlst[positionOfMax]:
                positionOfMax = location

        temp = mlst[fillslot]
        mlst[fillslot] = mlst[positionOfMax]
        mlst[positionOfMax] = temp

def dictsort(list, idd):
    for fillslot in range(len(list) -1, 0 , -1):
        positionOfMax = 0
        for location in range(1, fillslot + 1):
            if list[location][idd] > list[positionOfMax][idd]:
                positionOfMax = location

        temp = list[fillslot]
        list[fillslot] = list[positionOfMax]
        list[positionOfMax] = temp

def wait():
    wait = input("\nPress <ENTER> to continue...")

def main():
    print("\n----- Menu -----")
    print("""A - Add user
D - Display Users
P - Play game
E - Exit""")
    ch = input("\n>> Enter your choice: ")
    while (1):
        if ch.lower()=='a':
            adduser()
        elif ch.lower()=='d':
            dispuser()
            wait()
            main()
            return False
        elif ch.lower()=='p':

            wn = turtle.Screen()
            wn.bgcolor("black")
            wn.title("Space Guardian")
            #wn.bgpic("space_invaders_background.gif")

            score = 0
            #draw score
            score_pen = turtle.Turtle()
            score_pen.speed(0)
            score_pen.color("white")
            score_pen.penup()
            score_pen.setposition(-290, 280)
            scorestring = "Score: %s" %score
            score_pen.write(scorestring, False, align="left", font=("Arial", 14, "normal"))
            score_pen.hideturtle()

            #shapes
            turtle.register_shape("invader.gif")
            turtle.register_shape("player.gif")
            #border
            border_pen = turtle.Turtle()
            border_pen.speed(0)
            border_pen.color("white")
            border_pen.penup()
            border_pen.setposition(-300,-300)
            border_pen.pendown()
            border_pen.pensize(3)
            for side in range(4):
                border_pen.fd(600)
                border_pen.lt(90)
            border_pen.hideturtle()


            #player
            player = turtle.Turtle()
            player.color("blue")
            player.shape("triangle")
            player.penup()
            player.speed(0)
            player.setposition(0,-250)
            player.setheading(90)

            playerspeed = 15



            #number of enemies
            number_of_enemies = 2
            #list of enemies
            enemies = []

            #add enemies to the list
            for i in range(number_of_enemies):
                enemies.append(turtle.Turtle())

            for enemy in enemies:
                enemy.color("red")
                enemy.shape("circle")
                enemy.penup()
                enemy.speed(0)
                x = random.randint(-200,200)
                y = random.randint(100,250)
                enemy.setposition(x,y)

            enemyspeed= 3




            #player weapon
            bullet = turtle.Turtle()
            bullet.color("yellow")
            bullet.shape("triangle")
            bullet.penup()
            bullet.speed(0)
            bullet.setheading(90)
            bullet.shapesize(0.5,0.5)
            bullet.hideturtle()

            bulletspeed = 25

            #weapon state
            # ready to fire and fire
            bulletstate = "ready"
            #move function

            def move_left():
                x = player.xcor()
                x -= playerspeed
                #player border boundary
                if x <- 280:
                    x= -280
                player.setx(x)

            def move_right():
                x = player.xcor()
                x += playerspeed
                #player border boundary
                if x > 280:
                    x= 280
                player.setx(x)

            #bullet fn.
            def fire_bullet():
                global bulletstate
                if bulletstate == "ready":
                    bulletstate = "fire"

                if not bullet.isvisible():
                    x = player.xcor()
                    y = player.ycor() + 10
                    bullet.setposition(x,y)
                    bullet.showturtle()

                #bullet above player
                x = player.xcor()
                y = player.ycor()
                bullet.setposition(x, y+10)
                bullet.showturtle()

            def isCollision(t1, t2):
                distance = math.sqrt(math.pow(t1.xcor()-t2.xcor(),2) + math.pow(t1.ycor()-t2.ycor(),2))
                if distance < 15:
                    return True
                else:
                    return False



            wn.listen()
            wn.onkeypress(move_left, "Left")
            wn.onkeypress(move_right, "Right")
            wn.onkeypress(fire_bullet,"space")


            #main game loop
            while True:

                for enemy in enemies:
                    #move enemy
                    x = enemy.xcor()
                    x += enemyspeed
                    enemy.setx(x)

                    #enemy boundary check
                    if enemy.xcor() > 280:
                        #move all enemies down
                        for e in enemies:
                            y = e.ycor()
                            y -= 40
                            e.sety(y)
                        #change direction
                        enemyspeed *= -1

                    if enemy.xcor() < - 280:
                        #move all enemies down
                        for e in enemies:
                            y = e.ycor()
                            y -= 40
                            e.sety(y)
                        #change direction
                        enemyspeed *= -1

                    #collision w bullet and enemy
                    if isCollision(bullet,enemy):
                        bullet.hideturtle()
                        bulletstate = "ready"
                        bullet.setposition(0, -400)
                        x = random.randint(-200,200)
                        y = random.randint(100,250)
                        enemy.setposition(x,y)

                        #update score
                        score += 10
                        scorestring = "Score: %s" %score
                        score_pen.clear()
                        score_pen.write(scorestring, False, align="left", font=("Arial", 14, "normal"))

                    if isCollision(player,enemy):
                        player.hideturtle()
                        enemy.hideturtle()
                        print("Game over")
                        break

                    #Boundary check
                    if enemy.xcor() > 300 or enemy.xcor() < -300:
                        print("GAME OVER")
                        t1 = turtle.Turtle()
                        t1.pencolor("#8e072b")
                        t1.hideturtle()
                        t1.penup()
                        t1.write("GAME OVER", align = "center", font=("Silkscreen",20))
                        t1.setposition(0,-350)
                        t1.penup()


                    if enemy.ycor() > 300 or enemy.ycor() < -300:
                        print("Game OVER")
                        t1 = turtle.Turtle()
                        t1.pencolor("#8e072b")
                        t1.hideturtle()
                        t1.penup()
                        t1.write("GAME OVER", align = "center", font=("Silkscreen",20))
                        t1.setposition(0,-350)
                        t1.penup()
                        quit()



                #move bullet
                if bulletstate == "fire":
                    y = bullet.ycor()
                    y += bulletspeed
                    bullet.sety(y)

                if bullet.ycor() > 275:
                    bullet.hideturtle()
                    bulletstate = "ready"

                if bullet.isvisible():
                    y = bullet.ycor() + bulletspeed
                    bullet.sety(y)


            wn.mainloop()
            delay = input("enter to finish")

        elif ch.lower()=='e':
            print("\nThank you for coming!")
            raise SystemExit()
        else:
            print("\n!!! Invalid input. Try again !!!\n")
            main()


main()