Python turtle invalid command (From Think Python book)

Question

I'm trying to follow along with the exercises in the "Think Python" book and ran into a problem trying to get turtle to work. Here is the exercise I'm on. (4.1)

The code they want me to execute looks like this:

import turtle
bob = turtle.Turtle()
print(bob)
turtle.mainloop()

bob.fd(100)
bob.lt(90)
bob.fd(100)

But when I execute it, the turtle doesn't move and I get the following error when I close the window:

Traceback (most recent call last):
    File "C:\Users\Phil\PycharmProjects\untitled\mypolygon.py", line 6, in <module>
        bob.fd(100)
    File "C:\Python\3.5\lib\turtle.py", line 1637, in forward
        self._go(distance)
    File "C:\Python\3.5\lib\turtle.py", line 1605, in _go
        self._goto(ende)
    File "C:\Python\3.5\lib\turtle.py", line 3158, in _goto
        screen._pointlist(self.currentLineItem),
    File "C:\Python\3.5\lib\turtle.py", line 755, in _pointlist
        cl = self.cv.coords(item)
    File "<string>", line 1, in coords
    File "C:\Python\3.5\lib\tkinter\__init__.py", line 2308, in coords
        self.tk.call((self._w, 'coords') + args))]
_tkinter.TclError: invalid command name ".1395635997272"

I'm not sure what the debugger is saying, and I can't really continue until I figure out where I went wrong. Any help would be greatly appreciated.

score 2 · Accepted Answer · edited May 23 '17 at 10:28

The bob.fd(100) line (and all following lines) will never be reached as the turtle.mainloop() call starts a loop (as its name implies).

Change your code so that it reads:

import turtle
bob = turtle.Turtle()
print(bob)

bob.fd(100)
bob.lt(90)
bob.fd(100)

And everything should work.

(Since you are not handling any events in your program, I would recommend not calling turtle.mainloop() for now; if you do want to follow the book's example, make sure to do as it says: "To draw a right angle, add these lines to the program (after creating bob and before calling mainloop)").

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Python turtle invalid command (From Think Python book)

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