[Tutor] Text Boxes - deleting and inserting

Danny Yoo dyoo at hkn.eecs.berkeley.edu
Sun Oct 24 01:29:26 CEST 2004

On Fri, 22 Oct 2004 seanf at email.arizona.edu wrote:

> First of all a quick intro: My name is Sean Fioritto. I'm a CS major at
> the University of Arizona. My dad has been trying to get me to learn
> Python since my freshman year...about 3 years ago. I was finally able to
> put all the books he gave me to use because we're using Python in my AI
> class - and I have to say that if it were possible to have a crush on a
> programming language, I would be drooling over Python at this point.

Hi Sean,

Welcome aboard!  Glad that you're enjoying Python.

> Here's the error (m is a model object):
> >>> v = CritterView.cView()
> >>> v.update(m)
> Traceback (most recent call last):
>   File "<pyshell#26>", line 1, in -toplevel-
>     v.update(m)
>   File "C:\home\projects\CritterView.py", line 18, in update
>     self.delete(1.0, END)
> NameError: global name 'END' is not defined

Ah, this one isn't too bad.  END is defined in the Tkinter module, so you
either need to fully qualify it:

    self.delete(1.0, Tkinter.END)

or yank it into the namespace, during the import:

    from Tkinter import Text, END

On a side note, there's a block of code here that can be improved:

>         self.s = ""
>         for self.i in range(self.myWidth):
>             for self.j in range(self.myHeight):
>                 self.s = self.s + model.getChar(self.i, self.j)
>             self.s = self.s + '\n'

Repeated string concatentation can be expensive, depending on how large
self.myWidth and self.myHeight gets.

You may want to use a "buffer"  approach to accumulate that string
variable instead. In Java, there's a java.lang.StringBuffer class that's
designed for doing this kind of accumulation.  Python has a similar
feature that using a string's built-in join() method:

>>> buffer = []
>>> buffer.append("hello, this is")
>>> buffer.append("\n")
>>> buffer.append("a test")
>>> ''.join(buffer)
'hello, this is\na test'

I hope this helps!

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