Thursday, August 20, 2009

user dict ^ internal dict in python - my guess

There are various terms for the same concept
- registry -- generic concept across languages. A class has a registry and an instance has a registry too.
- namespace -- has special meaning in python, but some veterans say the various registries are implemented same as a namespace
- idic

2 types of dictionaries in python --

A) user dictionary are dictionaries you create
B) "idic" meaning "internal dict" is a building block of python objects, (possibly) including user dictionary objects.

A user dict is usually taught as an object with methods and fields. I hope that's not over simplification.

A namespace for a module, or class or anything is implemented as an idic. Accessed as whatever.__dict__. In a twist for consistency and coherence, this idic can be *used* as a regular user dictionary. You can do whatever.__dict__.keys(). You may rightly feel that a __dict__ is implemented the same as a user dictionary, but I doubt it.

Even if a __dict__ is implemented the same way as a user dict, I strongly believe beginners better treat them as 2 distinct things unrelated to each other, though the syntax looks similar.

Internal dict is the basis of python objects[3].  I guess a idic is more like a small expandable hash table [2]. Must be small because a *concrete* idic instance exists in EVERY parent class, subclass, and EVERY instance[1] of EVERY class.

[1] It's not too wrong to say it resembles the C struct.
[2] a perl object IS nothing but a hashtable or associative array. See the camel book. In php, an object is implemented as an associative array (or simply an "array").
[3] at least user defined objects

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