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5.3.1 Attribute references

An attribute reference is a primary followed by a period and a name:

      attributeref:   primary "." identifier

The primary must evaluate to an object of a type that supports attribute references, e.g., a module or a list. This object is then asked to produce the attribute whose name is the identifier. If this attribute is not available, the exception `AttributeError` is raised. Otherwise, the type and value of the object produced is determined by the object. Multiple evaluations of the same attribute reference may yield different objects.