Created by: zhhsplendid

1. Considering functions, I have to change the node type from single value to a set. Because python function is allowed to return different types. The set represent all possible types

2. I added scope_name and scope_type for AstVarScope, because in python functions, variable may have different scope. For example:

a = 3
def foo(b):
    a = 9
    return a + b

the a in foo is different to the a out of foo. Similar to class field. The scope_name will help me to know the function name when static analysis finds a return sentence.