Fix core dump in example from Samuele Pedroni: from __future__ import nested_scopes x=7 def f(): x=1 def g(): global x def i(): def h(): return x return h() return i() return g() print f() print x This kind of code didn't work correctly because x was treated as free in i, leading to an attempt to load x in g to make a closure for i. Solution is to make global decl apply to nested scopes unless their is an assignment. Thus, x in h is global.