Python's Reference And Internal Model Of Computing Languages

Xah Lee xahlee at gmail.com
Wed Feb 3 02:28:10 CET 2010


just wrote this essay. Comment & feedback very welcome.

Python's Reference And Internal Model Of Computing Languages

Xah Lee, 2010-02-02

In Python, there are 2 ways to clear a hash: “myHash = {}” and
“myHash.clear()”. What is the difference?
↓

The difference is that “myHash={}” simply creates a new empty hash and
assigns to myHash, while “myHash.clear()” actually clear the hash the
myHash is pointing to.

What does that mean?? Here's a code that illustrates:

# python
# 2 ways to clear hash and their difference
aa = {'a':3, 'b':4}
bb = aa
aa = {}
print bb # prints {'a': 3, 'b': 4}

aa = {'a':3, 'b':4}
bb = aa
aa.clear()
print bb # prints {}

This is like this because of the “reference” concept. The opposite
alternative, is that everything is a copy, for example in most
functional langs. (with respect to programer-visible behavior, not how
it is implemented)

>From the aspect of the relation of the language source code to the
program behavior by the source code, this “reference”-induced behavior
is similar to dynamic scope vs lexicol scope. The former being un-
intuitive and hard to understand the latter more intuitive and clear.
The former requires the lang to have a internal model of the language,
the latter more correspond to source code WYSIWYG. The former being
easy to implement and is in early langs, the latter being more popular
today.

As with many languages that have concept of references, or pointers,
this is a complexity that hampers programing progress. The concept of
using some sort of “reference” as part of the language is due to
implementation efficiency. Starting with C and others in 1960s up to
1990s. But as time went on, this concept in computer languages are
gradually disappearing, as they should.

Other langs that have this “reference” concept as ESSENTIAL part of
the semantic of the language, includes: C, C++, Java, Perl, Common
Lisp. (of course, each using different terminologies, and each lang
faction will gouge the other faction's eyes out about what is the true
meaning of terms like “reference”, “object”, “list/sequence/vector/
array/hash”, and absolutely pretend other meanings do not exist.
(partly due to, their ignorance of langs other than their own, partly,
due to male power struggle nature.))

Languages that do not have any “reference” or “object”, or otherwise
does not require the programer to have some internal model of source
code, are: Mathematica, JavaScript, PHP. (others may include TCL,
possibly assembly langs.)

For some detail on this, see: Jargons And High Level Languages and
Hardware Modeled Computer Languages.

---------------------------

(perm url of this essay can be found on my website.)

  Xah
∑ http://xahlee.org/


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