Collections of non-arbitrary objects ?

[walterbyrd]

On Jun 24, 10:31 pm, Bruno Desthuilliers
<bdesth.quelquech... at free.quelquepart.fr> wrote:

> > Especially since variables in python do not have to be explicitly
> > assigned
>
> ???

I have probably expressed this incorrectly. What I meant was:

>>> a = [1,2,3]
>>> b = a
>>> a[1] = 'spam'

Here, I have changed b, without an explicit assignment. After I
assigned a to b, I never did another "b =" yet b changed anyway
because I changed a. I am not saying there is anything wrong with
this, I'm just explaining what I meant.

So let's say I have list L, and I have a routine that expects every
item in L to be a dictionary like: {'name':'joe', 'job':'dev', 'pay':
min_wage}.

Not only could the app crash if an incorrect item where inserted into
L. But the app could crash if an incorrect item were inserted in lists
X,Y, or Z.

Of course, you can always work around this by just  programming very
carefully, and doing a lot of error checking. That is always true in
any language.

But, I think sometimes it's helpful to use a structure that is little
more restrictive, to sort of enforce a degree of integrity. An example
I have already given: why use tuples instead of a list? Tuples are
actually a bit more restrictive.

I don't think there is anything wrong with the data structures that
exist in python. I was just wondering if there was a structure that
would restrict a collection to only allow certain types. The
"restrictedlist" class discussed in another thread may be the sort of
thing I was looking for.

BTW: I think polymorphism is great and all. But it does have (and IMO
should have) it's limitations. For example, I don't think you can
divide a string by another string.