Hi,
In ChainMap example
c = ChainMap()        # Create root context
d = c.new_child()     # Create nested child context
e = c.new_child()     # Child of c, independent from d
e.maps[0]             # Current context dictionary -- like Python's locals()
e.maps[-1]            # Root context -- like Python's globals()
e.parents             # Enclosing context chain -- like Python's nonlocals

d['x']                # Get first key in the chain of contexts
d['x'] = 1            # Set value in current context

d['x'] - will raise key does not exist error 

so simple fix is to flip last two lines...

I know, possibly anal but look love Python and would like to help new folks to not get confused if they play with example in cPython shell...

--best