Turtle demo

[DavideGolinelli]

BPO	40113
Nosy	@stevendaprano
Files	spike.py backwards.png

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-03-30.11:32:25.926>
labels = ['3.7', 'type-bug', 'tests']
title = 'Turtle demo'
updated_at = <Date 2020-04-01.07:08:17.899>
user = 'https://bugs.python.org/DavideGolinelli'

bugs.python.org fields:

activity = <Date 2020-04-01.07:08:17.899>
actor = 'Davide Golinelli'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tests']
creation = <Date 2020-03-30.11:32:25.926>
creator = 'Davide Golinelli'
dependencies = []
files = ['49011', '49012']
hgrepos = []
issue_num = 40113
keywords = []
message_count = 6.0
messages = ['365303', '365306', '365308', '365310', '365444', '365451']
nosy_count = 2.0
nosy_names = ['steven.daprano', 'Davide Golinelli']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40113'
versions = ['Python 3.7']

[DavideGolinelli]

running the attacched simple program the turtle go backwards even if not asked.

i added a sleep command in order to view the bug more easly

[stevendaprano]

Perhaps this is just my old eyes, but I can't see where the turtle is going backwards. I can see it spinning, but it's not clear that the turtle position is moving backwards or if it is an illusion caused by the turtle spinning around.

If your eyes are better and can see the backward motion, perhaps you could adjust the drawing to make it more obvious. Hide the turtle and change the pen colour perhaps?

[stevendaprano]

Try changing the turtle to the arrow pointer and see if you can still see backwards movement.

    james.shape('arrow')

[DavideGolinelli]

I attacched a picture where you can see the cursor drawing backwars.

the program is supposed to draw a function like y=sin(x) but is drawing y=abs(sin(x)).

[stevendaprano]

the program is supposed to draw a function like y=sin(x) but is drawing y=abs(sin(x)).

It would have been nice if you had described the problem this way from your initial bug report, instead of saying that the turtle was moving backwards. I understood "moving backwards" as it going back over its own path, retracing its steps. I wasted a lot of time peering carefully at the screen trying to see where the turtle was retracing its steps.

Now I understand you mean the turtle is moving in the opposite direction from that it is facing. Gotcha.

You titled this bug report "Turtle demo", but I can't find it listed in the turtle demo here:

https://docs.python.org/3/library/turtle.html#module-turtledemo

Where did you get this demo from? If it's not from the standard library, you should report this to the author, as it is a bug in their code, not the turtle module, caused by mishandling of negative numbers. If you move *forward* by a *negative* amount, of course you are going in the opposite direction to that you are facing.

So the spike() function is buggy. There are probably many ways to fix it, depending on what you intend it to do, but probably the simplest is to just add a call to abs() before calling forward:

    james.forward(abs(int(d*100)))

[DavideGolinelli]

you're absolutely right!
I'm so sorry for wasting your time.

thanks and regards