[Tutor] Python and Tkinter (total newbie)

[Alan Gauld]

On 09/12/11 19:03, Richard Lyons wrote:
> I have tried to enter the first sample program from p. 19 in Grayson:
> Python and Tkinter Programming. When I run the program I get an error
> as follows:
>
> Traceback (most recent call last):
> File "/home/dick/Desktop/calc1.py", line 50, in <module>
> if _name_ == '_main_':
> NameError: name '_name_' is not defined
>
> The error makes sense because nowhere in the code is _main_ defined.

Read the error again. It is actually _name_ that it is complaining 
about! However, neither _name_ or "_main_" (notoice the quotes!) are 
defined.

The real problem is that you need a double underscore on each side. This 
is a special convention that is used in Python to indicate special 
"magic" being performed by Python behind the scenes.

In this case the magic variable __name__ is assigned the name of the 
file if the file is used as a module but the name "__main__" if the file 
is run as  a program. (In python there is no real difference between 
programs and module files. One file can do both jobs)

You will come across several other magic names as you explore python, 
most notably __init__ when looking at classes.

One thing to beware. Grayson's book is based on a very old version of 
Python so some things may have changed a little. If you hit 
unexplainable errors post them here and we can probably help you over 
them. Also Grayson's book takes no prisoners in its code. There is a lot 
of it and he assumes you know Python and GUI programming in general 
quite well. You may want to go through the standard Python tutorials 
before plunging too far into Tkinter!

HTH,


-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/