Tkinter, add pressed buttons onto string display string, how to?

Steve Holden steve at holdenweb.com
Sun Apr 6 04:24:33 CEST 2008


7stud wrote:
>>> Just like the message says: You are trying to use `str` (on the right hand
>>> side of the assignment) before anything is bound to that name.
>>> Ciao,
>>>         Marc 'BlackJack' Rintsch
>> i know but i want the variable str(which i found out is a reserved
>> word so i changed it) to be accessible all over __init__ right?
>>
> 
> "all over __init__" ? You could practice with a trivial example to
> discover how things work in python:
> 
> def f():
>     num = 10
>     print num
> 
> f()
> 
> def g():
>     print num
>     num = 10
> 
> g()
> 
> 
>> so i tried to delcare it in __init__ in the beginning of the framework
>> class but then when i access it in the method Display i get that
>> error.
>>
>> so how should i declare this variable to be able to access it
>> everywhere?
>>
> 
> You don't declare variables in python.  You just start using a
> variable when you need it.  In other words you don't do this:
> 
> string my_str
> my_str = "hello"
> 
> You just write:
> 
> my_str = "hello"
> 
> 
>> i want another method "calculate" that can access the same string
>> later and do the calculations(writing some other code now that will
>> read and interpret that).
> 
> Does this look familiar:
> 
>> Another thing you should be aware of: self is like a class wide
>> bulletin board. If you are writing code inside a class method, and
>> there is data that you want code inside another class method to be
>> able to see, then post the data on the class wide bulletin board, i.e.
>> attach it to self.  But in your code, you are doing this:
>>
>> self.btnDisplay = Button(self, text="7", default=ACTIVE)
>> self.btnDisplay.grid(row=5, column=0, padx=5, pady=5)
>>
>> self.btnDisplay = Button(self, text="8", default=ACTIVE)
>> self.btnDisplay.grid(row=5, column=1, padx=5, pady=5)
>>
>> As a result, your code continually overwrites self.btnDisplay.  That
>> means you aren't preserving the data assigned to self.btnDisplay.
>> Therefore, the data does not need to be posted on the class wide
>> bulletin board for other class methods to see.  So just write:
>>
>> btnDisplay = Button(self, text="7", default=ACTIVE)
>> btnDisplay.grid(row=5, column=0, padx=5, pady=5)
>>
>> btnDisplay = Button(self, text="8", default=ACTIVE)
>> btnDisplay.grid(row=5, column=1, padx=5, pady=5)

To pick nits, "str" is not a reserved word (normally referred to in 
Python as s "keyword"). It's perfectly possible to write:

 >>> def str(x):
...   return "Fooled you!"
...
 >>> str(3.14148)
'Fooled you!'
 >>>

and have your program work. But it's not generally good practice to 
*shadow* built-in names, even when nothing stops you from doing so, 
simply because there is usually a group somewhere with an investment in 
  using the standard names, and you will make their lives more difficult.

regards
  Steve
-- 
Steve Holden        +1 571 484 6266   +1 800 494 3119
Holden Web LLC              http://www.holdenweb.com/




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