matplotlib-devel Mailing List for matplotlib

On Tue, Oct 25, 2011 at 3:52 PM, Daniel Hyams <dh...@gm...> wrote:
> For small bugfixes, am I supposed to fork from v1.1.x, or master?
I say 'master' (Mike's been pushing some things to v1.1.x, but as he
said in a comment to #551, "Pushed to v1.1.x since this is pretty
serious yet simple-to-fix bug -- it should be on the maintenance
branch.")
best,
-- 
Paul Ivanov
314 address only used for lists, off-list direct email at:
http://pirsquared.org | GPG/PGP key id: 0x0F3E28F7

On Tuesday, October 25, 2011, Daniel Hyams <dh...@gm...> wrote:
> For small bugfixes, am I supposed to fork from v1.1.x, or master?
>
V1.1.x is the maintenance branch. Master is for new features. When
bugfixes are made and merged to v1.1.x, we then merge it to master.
Ben Root

For small bugfixes, am I supposed to fork from v1.1.x, or master?
-- 
Daniel Hyams
dh...@gm...

Daniel -
Yes that works. In my case - I hate to edit any existing third party 
code bases - or it bites me later when I upgrade.
For now - I simply do my own dead reference clean up externally when 
doing the deletes. Really, that would be the same as just doing a 
disconnect - but for other reasons (not worth going into detail here) 
- I prefer deleting and not having to know all of the connection 
points. My solution ensures that the dead references aren't around 
later.
I mainly wanted to get it out into the devel community - get smart 
eyeballs on it - and hope that it gets addresses in a future release.
It will likely be a fairly straightforward fix - as you show.

I've run into this same issue in the past, and have it "fixed" in my
own local copy of matplotlib. I just placed a check to make sure that
cid actually was in the callbacks for s before deleting it.
That is quite possibly a band-aid; I never looked far enough in to
see. But it is possibly another way of fixing the problem.
 def process(self, s, *args, **kwargs):
 """
 process signal *s*. All of the functions registered to receive
 callbacks on *s* will be called with *\*args* and *\*\*kwargs*
 """
 if s in self.callbacks:
 for cid, proxy in self.callbacks[s].items():
 # Clean out dead references
 if proxy.inst is not None and proxy.inst() is None:
 if cid in self.callbacks[s]: #<------- here
 del self.callbacks[s][cid]
 else:
 proxy(*args, **kwargs)
On Tue, Oct 25, 2011 at 1:09 PM, <to...@i3...> wrote:
> Here is a bit more detail and a simple example.
>
> The example below places red squares in an axes. When the user clicks on an existing red square - another square is created and added. When the user hits any key a square is deleted from the axes. The error is triggered by clicking on the red square and then hitting any key, and then clicking a red square again.
>
> Diagnosis:
> By monitoring cbook.py line 235 and cbook.py line 263 it can be seen that after the second mouse click (following one of the squares being deleted), that the process() function builds a loop and begins handling the button press callbacks. Note that there is a dead reference coming later in this list. The first callback involves another square being created and the connect() method being called. In the connect() call - the dead reference is deleted from the callback list. Now upon returning to the process() callback this dead reference is no longer in the callback list and a Key Exception is triggered once it gets to it in the loop.
>
> Problem:
> There are two locations where dead references are cleared from the callback list. When these loops get intermingled - as the case with a callback leading to another connect mid-loop - the exception occurs when both loops attempt to delete the dead reference.
>
> Possible Solutions:
> 1. Trap the KeyException at the point of attempting to delete it from the list in both places.
>
> 2. Place the dead reference check and deletion within a single method ... and perform this check at beginning of the process() and connect() methods before processing callbacks.
>
>
> Sample Code
> --------------------
>
> import matplotlib
> matplotlib.use('WXAGG')
>
> from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg
> from matplotlib.pyplot import Figure, Axes, Rectangle
>
> import wx
> import random
>
> class SquareManager(object):
>  def __init__(self, axes):
>    self.axes = axes
>    self.canvas = axes.figure.canvas
>    self.squares = []
>    self.last_x = 0
>
>    self.canvas.mpl_connect('key_press_event', self.on_key_press)
>
>  def add_square(self):
>    self.last_x += .1
>    s = Square(self, self.axes, [self.last_x, .4],
>          .05, .05, facecolor='red', edgecolor='black')
>    self.squares.append(s)
>    self._refresh()
>
>  def on_key_press(self, evt):
>    if len(self.squares) == 0: return
>
>    # delete the first square - results in no error
>    # self.squares[0].remove()
>    # del self.squares[0]
>
>    # delete the last square - results in the error
>    self.squares[-1].remove()
>    del self.squares[-1]
>
>    self._refresh()
>
>  def _refresh(self):
>    self.canvas.draw()
>
>
> class Square(Rectangle):
>  def __init__(self, manager, axes, *args, **kwds):
>    Rectangle.__init__(self, *args, **kwds)
>    axes.add_patch(self)
>
>    self.manager = manager
>    axes.figure.canvas.mpl_connect('button_press_event', self.selected)
>
>  def selected(self, evt):
>    within, _ = self.contains(evt)
>    if within:
>      self.manager.add_square()
>
>
> app = wx.PySimpleApp()
> frame = wx.Frame(None)
> fig = Figure()
> canvas = FigureCanvasWxAgg(frame, -1, fig)
> a = Axes(fig, [.1, .1, .8, .8])
> fig.add_axes(a)
>
> sm = SquareManager(a)
> sm.add_square()
>
> frame.Show()
> app.MainLoop()
>
>
> # To demonstrate the error:
> #
> # 1. click on red sqaure
> # 2. press any key
> # 3. click on red sqaure again
>
>
>
>
>
>
>
>
>
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-- 
Daniel Hyams
dh...@gm...

Here is a bit more detail and a simple example.
The example below places red squares in an axes. When the user clicks on an existing red square - another square is created and added. When the user hits any key a square is deleted from the axes. The error is triggered by clicking on the red square and then hitting any key, and then clicking a red square again.
Diagnosis:
By monitoring cbook.py line 235 and cbook.py line 263 it can be seen that after the second mouse click (following one of the squares being deleted), that the process() function builds a loop and begins handling the button press callbacks. Note that there is a dead reference coming later in this list. The first callback involves another square being created and the connect() method being called. In the connect() call - the dead reference is deleted from the callback list. Now upon returning to the process() callback this dead reference is no longer in the callback list and a Key Exception is triggered once it gets to it in the loop.
Problem:
There are two locations where dead references are cleared from the callback list. When these loops get intermingled - as the case with a callback leading to another connect mid-loop - the exception occurs when both loops attempt to delete the dead reference.
Possible Solutions:
1. Trap the KeyException at the point of attempting to delete it from the list in both places.
2. Place the dead reference check and deletion within a single method ... and perform this check at beginning of the process() and connect() methods before processing callbacks.
Sample Code
--------------------
import matplotlib
matplotlib.use('WXAGG')
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg
from matplotlib.pyplot import Figure, Axes, Rectangle
import wx
import random
class SquareManager(object):
 def __init__(self, axes):
 self.axes = axes
 self.canvas = axes.figure.canvas 
 self.squares = []
 self.last_x = 0
 
 self.canvas.mpl_connect('key_press_event', self.on_key_press)
 
 def add_square(self):
 self.last_x += .1
 s = Square(self, self.axes, [self.last_x, .4],
 .05, .05, facecolor='red', edgecolor='black')
 self.squares.append(s)
 self._refresh()
 
 def on_key_press(self, evt):
 if len(self.squares) == 0: return
 
 # delete the first square - results in no error
 # self.squares[0].remove()
 # del self.squares[0]
 
 # delete the last square - results in the error
 self.squares[-1].remove()
 del self.squares[-1]
 
 self._refresh()
 
 def _refresh(self):
 self.canvas.draw()
class Square(Rectangle):
 def __init__(self, manager, axes, *args, **kwds):
 Rectangle.__init__(self, *args, **kwds)
 axes.add_patch(self)
 
 self.manager = manager
 axes.figure.canvas.mpl_connect('button_press_event', self.selected)
 
 def selected(self, evt):
 within, _ = self.contains(evt)
 if within:
 self.manager.add_square()
app = wx.PySimpleApp()
frame = wx.Frame(None)
fig = Figure()
canvas = FigureCanvasWxAgg(frame, -1, fig)
a = Axes(fig, [.1, .1, .8, .8])
fig.add_axes(a)
sm = SquareManager(a)
sm.add_square()
 
frame.Show()
app.MainLoop()
# To demonstrate the error:
#
# 1. click on red sqaure
# 2. press any key
# 3. click on red sqaure again