John Gunderman wrote: > I am new to python and have found both the concept of namespaces and the > __dict__ function to be rather confusing, and I cant find any good > explanations on the web. Could any of you give me a good explanation of > these? And for __dict__, is is the same thing as __str__ except in > string form, or does it store all current objects of that class in a > __dict__?
First, __dict__ is an attribute of an object whose value is a dict, not a function. A namespace is a place where names can be defined. The official tutorial says, A namespace is a mapping from names to objects. Most namespaces are currently implemented as Python dictionaries... Examples of namespaces are: the set of built-in names (functions such as abs(), and built-in exception names); the global names in a module; and the local names in a function invocation. In a sense the set of attributes of an object also form a namespace. http://docs.python.org/tut/node11.html#SECTION0011200000000000000000 Another way to think of it is, a namespace is a place where names are looked up. When you use a bare name (not an attribute), it is looked up in the local namespace, then the global namespace, then the built-in namespace. For example: y = 2 # Defines y in the global (module) namespace def f(): x = 1 # Defines x in the local (function) namespace # This looks up x, finds it in the local namespace # looks up abs, finds it in the built-in namespace print abs(x) # This looks up y, finds it in the global namespace print y Note that none of the above namespaces have a related __dict__ attribute, the namespace mappings are not stored that way. Objects also define a sort of namespace, where attributes are defined and looked up. The dict containing the namespace of an object is itself stored as an attribute of the object, called __dict__. So __dict__ is an implementation detail of the way object attributes are stored. As a beginner, it is important to understand the way bare names are looked up (local, global, built-in namespace) and a bit about the way attributes work. You don't have to be concerned with the implementation details such as __dict__. (For completeness, I will say that the full attribute lookup model is much more complicated than I have indicated above. I have simplified to focus on __dict__.) Kent _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
