[Tutor] click and line

[Shi Mu]

it works now.

from Tkinter import *

root = Tk()

c = Canvas(root, bg='#0e2e0e', height=500, width=1000)
frame = c
lastX=""
lastY=""
def click(event):
  global lastX, lastY
  if lastX != "":
     c.create_line(lastX,lastY,event.x,event.y,fill="white")
  lastX = event.x
  lastY = event.y


c.bind('<Button-1>',click)

c.pack()

root.mainloop()

On 11/6/05, Shi Mu <samrobertsmith at gmail.com> wrote:
> based on the following rewritten code, why the lines still can not be
> drawn? (there is no error report and the canvas appears).
>
> from Tkinter import *
>
> root = Tk()
>
> c = Canvas(root, bg='#0e2e0e', height=500, width=1000)
>
> lastX=""
> lastY=""
> def click(event):
>  global lastX, lastY
>  if lastX != "":
>     c.create_line(lastX,lastY,event.x,event.y,fill="white")
>  lastX = event.x
>  lastY = event.y
>
> frame = c
> c.bind('<Button-1>',click)
>
> c.pack()
>
> root.mainloop()
>
> On 11/6/05, Danny Yoo <dyoo at hkn.eecs.berkeley.edu> wrote:
> >
> > Hi Shi Mu,
> >
> > Let's look at click():
> >
> > ##########################
> > def click(event):
> >    print event.x, event.y
> >    m1=event.x
> >    n1=event.y
> > ##########################
> >
> > By default, variable names in functions are local.  Do you know about
> > local vs global variables?  The assignments to m1 and n1 won't be
> > remembered once we come out of the click() function.
> >
> >
> > It sounds like you want a function-like thing that remembers the very last
> > event we passed to it before.  One way to do this is to use globals,
> > because globals last beyond function calls.
> >
> > For example:
> >
> > ######
> > >>> n = None
> > >>> def lastNumber(x):
> > ...     global n
> > ...     print "I last saw", n
> > ...     n = x
> > ...
> > >>> lastNumber(42)
> > I last saw None
> > >>> lastNumber(17)
> > I last saw 42
> > >>> lastNumber(3)
> > I last saw 17
> > ######
> >
> > So for something very simple, using a global will probably be easiest.
> >
> >
> > However, there are other approaches that don't use globals. One that fits
> > Python's model well is to use a class instance, since instances can store
> > state:
> >
> > ######
> > >>> class LastNumber:
> > ...     def __init__(self):
> > ...         self.n = None
> > ...     def getAndSet(self, x):
> > ...         value = self.n
> > ...         self.n = x
> > ...         return value
> > ...
> > >>> last = LastNumber()
> > >>> last.getAndSet(42)
> > >>> last.getAndSet(3)
> > 42
> > >>> last.getAndSet(7)
> > 3
> > >>> last.getAndSet(9)
> > 7
> > ######
> >
> >
> > Does this make sense?  Please feel free to ask questions here.
> >
> >
>