turtle defined function not executing all code at once

user_17441211 0
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I'm trying to write a program that allows me to plot some simple coordinates using the turtle module and to make it more user friendly I wanted display a cross every time the user pressed the left mouse button to plot a point. For some reason the last bit of the cross() function ie. the last line of the cross won't draw or come up until the left mouse button is pressed again. I'm really confused as to why this is happening because the code is definitely being executed. Any help would be greatly appreciated!


wn = t.Screen()
wn.title("graph")
wn.setup(width=600, height=600)
wn.tracer(0)
wn.update()

pen = t.Turtle()
pen.color("black")
pen.shape("classic")
pen.goto(0, 0)
pen.ht()

x = 10
y = 10

def cross(x, y):
    print(x, y)
    pen.pensize(2.5)
    pen.pu()
    pen.goto(x, y)
    pen.pd()
    pen.seth(225)
    pen.color("red")
    pen.fd(50)
    pen.color("black")

    pen.pu()
    pen.goto(x, y)
    pen.pd()
    pen.left(180)
    pen.fd(50)

    pen.pu()
    pen.goto(x, y)
    pen.seth(315)
    pen.pd()
    pen.color("green")
    pen.fd(50)

    pen.pu()
    pen.goto(x, y)
    pen.left(180)
    pen.pd()
    pen.color("yellow")
    pen.fd(50) #for some reason this is not being done
    print("now")

cross(x, y)

while True:
    wn.update()
    wn.onscreenclick(cross)
    wn.mainloop()
python-turtle turtle-graphics python
1 Answers

This code indicates a basic misunderstanding of what onscreenclick() and mainloop() do:

while True:
    wn.update()
    wn.onscreenclick(cross)
    wn.mainloop()

Let's rework the code to use these methods correctly, and fix the problem:

from turtle import Screen, Pen

def cross(x, y):
    screen.onclick(None)  # disable handler inside handler

    pen.penup()
    pen.goto(x, y)
    pen.pendown()
    pen.setheading(225)
    pen.color('red')
    pen.forward(50)

    pen.penup()
    pen.goto(x, y)
    pen.pendown()
    pen.left(180)
    pen.color('black')
    pen.forward(50)

    pen.penup()
    pen.goto(x, y)
    pen.seth(315)
    pen.pendown()
    pen.color('green')
    pen.forward(50)

    pen.penup()
    pen.goto(x, y)
    pen.left(180)
    pen.pendown()
    pen.color('yellow')
    pen.forward(50)

    screen.update()
    screen.onclick(cross)  # reenable handler on exit

screen = Screen()
screen.title("graph")
screen.setup(width=600, height=600)
screen.tracer(0)

pen = Pen()
pen.hideturtle()
pen.color('black')
pen.pensize(2.5)

x, y = 10, 10

screen.onclick(cross)

cross(x, y)

screen.mainloop()

Generally, I would avoid using tracer() and update() until your code is basically working. Putting them in from the start makes your code harder to debug.

user_57712690
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