On Thu, 05 Feb 2009 01:36:17 -0000, Vincent Davis
<vinc...@vincentdavis.net> wrote:
if I start with
M = [1,3,5,7]
M is [1,3,5,7]
This seems one way, as [1,3,5,7] is not M in the sense that there is
no operation I can preform on [1,3,5,7] and get M back. Other than
asking/testing M==[1,3,5,7]
Correct. If you actually try that, you get this:
Python 2.5.2 (r252:60911, May 7 2008, 15:21:12)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
M = [1,3,5,7]
M is [1,3,5,7]
False
This isn't just me being funny with your suggested syntax, it's
making an important point: the second [1,3,5,7] is an entirely
different object to the list we named M, it just happens to
contain the same data.
This seems fine to me. but when I savedata(M) it seems I should be
able to refer to both [1,3,5,7] and "M", "I mean I did just type it
why type it again)
My argument comes down to; we use M so we don't have to type
[1,3,5,7], I realize that this is in part because we might not no what
M will be.
That's an oversimplification, and you're battering away well past the
point where it works. In any language, not just Python.
This is starting to sound like double talk on my part, I have only
been programing in python for 2 weeks so my credibility is only that
of an outside that MAY have a reasonable way of thinking of this or at
least a feature I would like.
The problem is you seem to be thinking in terms of objects having names.
They don't. Names have objects.
What I mean by that is that when you type "M = [1,3,5,7]", you are saying
"when I say 'M', substitute in this list (not just one that looks like it,
this exact list". When you type "N = M", similarly you get the name N
bound to the same exact list; if you then type "N[1] = 2" and print out
M, it'll show up as [1,2,5,7] -- it's still the same list under both names.
In effect (to oversimplify more than a bit), Python looks up the name
in a dictionary to get the object it represents.
The reverse lookup doesn't exist, largely because it isn't unique. Our
[1,3,5,7] list has no idea what names, if any, refer to it, and in all
but the most trivial cases the information isn't really meaningful.
Suppose that we did have a "getvariablename" function, what would you
expect the following code to do?
def f(thing):
print getvariablename(thing)
m = [1,3,5,7]
for n in m:
f(n)
Should it say "n" for all of them? Or "['n', 'thing']", since 'thing'
is after all a perfectly valid name for it?
Then what about this:
for i in range(len(m)):
f(m[i])
Should it say "m[i]" for all of them, or "m[0]" "m[1]" and so on, or
what?
by the way what is "**kwargs" I can't find any documentation on this?
http://docs.python.org/tutorial/controlflow.html#keyword-arguments
In a function definition, "**name" mops up all the keyword arguments
to the function that aren't explicit formal parameters into a
dictionary called "name", indexed by keyword. "kwargs" seems to be
the traditional name to use. So:
def demo(action, **kwargs):
... print kwargs
...
demo(action="dummy", text="wombats are go")
{'text': 'wombats are go'}
You can also use it the other way round to expand a dictionary into
keyword parameters to a function call:
myargs = { 'action': 'avoid', 'where': 'Camelot', 'because': 'it is a
silly place' }
demo(**myargs)
{'because': 'it is a silly place', 'where': 'Camelot'}
--
Rhodri James *-* Wildebeeste Herder to the Masses
--
http://mail.python.org/mailman/listinfo/python-list
