[Solved] Collisions aren’t registering with Python Turtles

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I think your primary issue is you’re updating the bullet between every enemy update instead of once for all the the enemy updates. This creates a skew between the visual and what’s really happening. Also, you don’t need to define the Pythagorean formula, turtles already know it! Below is my rework of your code to address the above and rework the the coding style and efficiency a bit:

from turtle import Turtle, Screen
from random import randint

NUMBER_OF_ENEMIES = 5
ENEMY_JUMP = 40

BULLET_SPEED = 20
PLAYER_SPEED = 15

SAFETY_DISTANCE = 15

GALLERY_WIDTH, GALLERY_HEIGHT = 560, 550
GALLERY_BORDER = 80

# player movement
def move_left():
    x = player.xcor() - PLAYER_SPEED

    if x < -GALLERY_WIDTH / 2:
        x = -GALLERY_WIDTH / 2

    player.setx(x)

def move_right():
    x = player.xcor() + PLAYER_SPEED

    if x > GALLERY_WIDTH / 2:
        x = GALLERY_WIDTH / 2

    player.setx(x)

def fire_bullet():
    global bulletstate

    if bulletstate == 'ready':
        bulletstate="fire"
        bullet.setposition(player.position())
        bullet.forward(BULLET_SPEED / 2)
        bullet.showturtle()

def isCollision(t1, t2):
    return t1.distance(t2) < SAFETY_DISTANCE

def move():
    global enemy_speed, bulletstate

    screen.tracer(False)

    for enemy in enemies:
        x = enemy.xcor() + enemy_speed

        enemy.setx(x)

        if x > GALLERY_WIDTH / 2:
            for e in enemies:
                y = e.ycor() - ENEMY_JUMP
                e.sety(y)

            enemy_speed *= -1

        elif x < -GALLERY_WIDTH / 2:
            for e in enemies:
                y = e.ycor() - ENEMY_JUMP
                e.sety(y)

            enemy_speed *= -1

        if isCollision(player, enemy):
            player.hideturtle()
            enemy.hideturtle()
            print("Get To The Doctors! You're Riddled!")
            screen.update()
            return

        if isCollision(bullet, enemy):
            # reset the bullet
            bullet.hideturtle()
            bullet.setposition(0, -GALLERY_HEIGHT)
            bulletstate="ready"

            # reset the enemy
            enemy.hideturtle()
            x = randint(GALLERY_BORDER - GALLERY_WIDTH / 2, GALLERY_WIDTH / 2 - GALLERY_BORDER)
            y = randint(GALLERY_HEIGHT / 2 - 175, GALLERY_HEIGHT / 2 - 25)
            enemy.setposition(x, y)
            enemy.showturtle()

    if bulletstate == 'fire':
        bullet.forward(BULLET_SPEED)

        # check to see if the bullets has gone to the top
        if bullet.ycor() > GALLERY_HEIGHT / 2:
            bullet.hideturtle()
            bulletstate="ready"

    screen.tracer(True)

    screen.ontimer(move, 25)

screen = Screen()
screen.setup(GALLERY_WIDTH + GALLERY_BORDER, GALLERY_HEIGHT + GALLERY_BORDER)
screen.bgcolor('black')

player = Turtle('turtle', visible=False)
player.speed('fastest')
player.color('red')
player.penup()
player.setheading(90)
player.sety(-250)  # need to define this
player.showturtle()

enemies = []

enemy_speed = 1

for _ in range(NUMBER_OF_ENEMIES):
    enemy = Turtle('circle', visible=False)
    enemy.speed('fastest')
    enemy.color('green')
    enemy.penup()

    x = randint(GALLERY_BORDER - GALLERY_WIDTH / 2, GALLERY_WIDTH / 2 - GALLERY_BORDER)
    y = randint(GALLERY_HEIGHT / 2 - 175, GALLERY_HEIGHT / 2 - 25)  # define these!
    enemy.setposition(x, y)
    enemy.showturtle()

    enemies.append(enemy)

# create the player's spunk shots
bullet = Turtle('triangle', visible=False)
bullet.speed('fastest')
bullet.shapesize(0.5)
bullet.color('white')
bullet.penup()
bullet.setheading(90)

# define bullet state
# ready - ready to fire
# fire - bullet is firing
bulletstate="ready"

screen.onkey(move_left, 'Left')
screen.onkey(move_right, 'Right')
screen.onkey(fire_bullet, 'space')

screen.listen()

move()

screen.mainloop()

I guessed at the missing pieces. See how this plays for you.

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solved Collisions aren’t registering with Python Turtles