declaring a global dynamic variable in python

For completeness, here's the answer to your original question. But it's almost certainly not what you meant to do -- there are very few cases where modifying the scope's dict is the right thing to do.

globals()[a] = 'whatever'

Instead of a dynamic global variable, use a dict:

movies = {}

a = 'BrokenCristals'

movies[a] = movieClass.shot()
movies[a].set_name(a)
# etc

The global keyword specifies that a variable you're using in one scope actually belongs to the outer scope. Since you do not have nested scopes in your example, global doesn't know what you're trying to do. See Using global variables in a function other than the one that created them