Steven D'Aprano
2/27/2010 3:34:00 AM
On Fri, 26 Feb 2010 15:32:27 -0800, Raphael Mayoraz wrote:
> Hello,
>
> I'd like to define variables with some specific name that has a common
> prefix.
> Something like this:
>
> varDic = {'red': 'a', 'green': 'b', 'blue': 'c'}
> for key, value in varDic.iteritems():
> 'myPrefix' + key = value
>
> I know this is illegal, but there must be a trick somewhere.
The Right answer is:
Don't do that. How can you use a variable without knowing its name?
Suppose you do this:
for key, value in varDic.iteritems():
'myPrefix_' + key = value
and then later you want:
print myPrefix_blue
But hang on. How could you possibly know it is called myPrefix_blue and
not myPrefix_cyan or myPrefix_turquoise?
You can't possibly know, so in general defining a named variable is
useless. What you want instead is:
some_colour = 'blue' # get this at runtime
print varDic[some_colour]
You don't even need the myPrefix, but if you really want it:
for key, value in varDic.iteritems():
varDic['myPrefix_' + key] = value
del varDic[key]
some_colour = 'blue' # get this at runtime
print varDic['myPrefix_' + some_colour]
or any one of a million variations on this idea.
For some very, very rare situations you might need to programatically
define variables. The right way to do that is:
globals()['myPrefix_turquoise'] = 42
or
setattr(module, 'myPrefix_turquoise'] = 42
or even:
exec "'myPrefix_turquoise' = 42"
but if you are thinking of using that last one with data coming from an
untrusted user (and nearly all users are untrusted!), then DON'T. That is
a huge security hole. And it's also very slow.
--
Steven