Ask for help about class variable scope (Re: Why doesn't a dictionary work in classes?)

[jfong]

I saw the code below at stackoverflow. I have a little idea about the scope of 
a class, and list comprehension and generator expressions, but still can't 
figure out why Z4 works and Z5 not. Can someone explain it? (in a 
not-too-complicated way:-)

class Foo():
    XS = [15, 15, 15, 15]
    Z4 = sum(val for val in XS)
    try:
        Z5 = sum(XS[i] for i in range(len(XS)))
    except NameError:
        Z5 = None

print(Foo.Z4, Foo.Z5)
>>> 60 None


--Jach
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