Question

I am trying to enable the user of my drawing program (written in python with pygame) to rename selected objects, then be able to access them through the live interpreter by their names. The following is a method of the base class of all drawable objects. When this code is run, I get no errors, but when I try to access the object through its new name, I am told that the variable with that name is not defined.
Any ideas why this might be?

def rename(self,newName):

    """
    Gives this drawable a new name by which the user my reference it in
    code
    """

    #Create a new variable in the global scope
    command =  'global ' + newName + '\n'

    #Tie it to me
    command += newName + ' = self' + '\n'

    #If I already had a name, I'll remove this reference
    if self.name != None:
        command += 'del ' + self.name

    #Execute the command
    exec(command)

    #Make this adjustment internally
    self.name = newName

Answer 1

I don’t think that will work, because the exec function has its own conecpt of global variables, independent of the one your function sees.

Generally speaking it is easier to manipulate the dictionary of the module. Note that the global scope is actually the member names of the current module.

For example, if you are using the __main__ module, to add a variable:

sys.modules['__main__'].__setattr__('xxx', 42)

And to delete it:

sys.modules['__main__'].__delattr__('xxx')

UPDATE: On second thought, if you don’t care about the module, it is better if you use the globals() dictionary. To add a variable:

globals()['xxx'] = 42

And to delete it:

del globals()['xxx']

Naturally, that is equivalent to the former, because globals() returns something like (sys.modules[__name__].__dict__).

Nifty. The conclusion is: if you use eval to do reflection, you are doing it wrong.