Question

I have the following setup in one module:

class A(object):
    # stuff

class B(object):
    # stuff

Now what I want to do is, creating an instance of class A by name (I just have the class name as a string) inside of B. How can I do this avoiding the globals function?

Answer 1

Why not just use A? Or do you have just a string 'A'? If yes, globals()['A'] is the way to go. The alternative would be getattr(sys.modules[__name__], 'A') but obviously globals() is more appropriate.

>>> dis.dis(lambda: getattr(sys.modules[__name__], 'Foo'))
  1           0 LOAD_GLOBAL              0 (getattr)
              3 LOAD_GLOBAL              1 (sys)
              6 LOAD_ATTR                2 (modules)
              9 LOAD_GLOBAL              3 (__name__)
             12 BINARY_SUBSCR
             13 LOAD_CONST               1 ('Foo')
             16 CALL_FUNCTION            2
             19 RETURN_VALUE

>>> dis.dis(lambda: globals()['Foo'])
  1           0 LOAD_GLOBAL              0 (globals)
              3 CALL_FUNCTION            0
              6 LOAD_CONST               1 ('Foo')
              9 BINARY_SUBSCR
             10 RETURN_VALUE

>>> dis.dis(lambda: Foo)
  1           0 LOAD_GLOBAL              0 (Foo)
              3 RETURN_VALUE

So by just looking at the instructions used for the various ways to access Foo, using globals() is most likely faster than going through sys.modules.