Very simple - please help

[Mark Tolonen]

"Chris Rebert" <clp at rebertia.com> wrote in message 
news:mailman.3681.1226121848.3487.python-list at python.org...
> On Fri, Nov 7, 2008 at 8:52 PM, pineapple <pineapple.link at yahoo.com> 
> wrote:
>> I am not a python programmer, but am being forced to port one of my
>> (smalltalk) applications to python for pragmatic reasons (python is
>> embedded with a graphics package I am switching over to, so to use the
>> graphics package I am essentially forced to use python).  Okay, enough
>> background.
>>
>> At any rate, in my smalltalk solution, in order to avoid an if-then-
>> else chain of "if this command, do this function, else if this command
>> do another function..." I have commands set up in a dictionary.  I
>> read the command integer, then key it into the dictionary to see what
>> method/function to call.
>>
>> #Conceptual representation of dictionary with keys and values:
>>
>> 1: do_command1
>> 2: do_command2
>> 3: etc...
>>
>> Trying to set up the same thing in python, it seems the lambda
>> expression is what I need.  So I set up a simple class to test this,
>> with some simple code as follows:
>>
>> ###
>> class Blah(list):
>>        pass
>>
>> commands = {1: (lambda: Blah())}
>> ###
>>
>> This is accepted by the interpreter, no problem.  If I type "commands"
>> into the interpreter I get the dictionary back showing the key '1'
>> attached to the lambda expression.  If I type "commands[1]" into the
>> interpreter, I get the lambda function back.  However, when I try to
>> invoke the lambda function with a "commands[1]()", I get a "global
>> name 'Blah' is not defined."  I find this error odd, because if I do a
>> "Blah()", I get back a "[]" as expected (a list).
>
> The code you gave works perfectly:
>
> chris ~ $ python
> Python 2.5.1 (r251:54863, Feb  4 2008, 21:48:13)
> [GCC 4.0.1 (Apple Inc. build 5465)] on darwin
> Type "help", "copyright", "credits" or "license" for more information.
>>>> class Blah(list):
> ...     pass
> ...
>>>> commands = {1: (lambda: Blah())}
>>>> commands[1]()
> []
>
> Please post some of the actual code so that we can determine the problem.
> Taking a guess, I'd suspect Blah and commands are in different modules
> and you didn't import Blah into commands' module, hence why Python
> can't find it. But we'd need some more details to be able to determine
> that.
>
> Cheers,
> Chris

Also, you don't need a lambda for this example:

>>> class Blah(list): pass
...
>>> d={1:Blah}
>>> d[1]()
[]

-Mark