Bad programming style?

[Gordon McMillan]

Sposhua wrote:

> I'm sure this is bad programming (though I'm sure I'll be proved
> wrong), but I'd like to know how to do it anyway...
> 
> I want to create a varaible name and use it as a normal variable,
> something like:
> 
> c=['r','g','b']
> VARIABLE_CALLED(c[0])='ff'
> 
> obviously there are ways around it using dictionaries or
> whatever, but I'd like to know if it's possible to actually
> _create_ this variable r='ff' 'on the fly'. And can anyone tell
> me if it actually has any use.

You can do it and you probably shouldn't. The problem is 
referencing it. How do you know what name to reference? If it 
hasn't been created, you'll get a NameError.

You probably should use a dictionary (namespaces in Python 
are dictionaries anyway(*)). That gives you syntax for looking 
for a non-existant name without taking a NameError, and an 
easy way to list out all the names you've created.

myvars = {}

if myvars.has_key('spam'): ...

value = myvars.get('spam', None) #None if doesn't exist

for var in myvars.keys(): ...

(*) The "locals" namespace is conceptually a dictionary, but 
gets optimized into something else.

You can use a dummy class for syntactic sugar:

class Dummy:
  pass

myvars = Dummy()

myvars.spam = 'eggs'

if hasattr(myvars, 'spam'): ...

for var in dir(myvars):

Be wary of "trying" too hard to do something dynamic. Python 
usually has a very direct way of doing it.

- Gordon