Adding to a module's __dict__?

[Roy Smith]

>From inside a module, I want to add a key-value pair to the module's
__dict__.  I know I can just do:

FOO = 'bar'

at the module top-level, but I've got 'FOO' as a string and what I
really need to do is

__dict__['Foo'] = 'bar'

When I do that, I get "NameError: name '__dict__' is not defined".  Is
it possible to do what I'm trying to do?