Python equivalent of Java Vector

[David Bolen]

hoopy_frood at my-deja.com writes:

> "Does Python have something equivalent to Java's Vector?  For instance,
> most of the time if you want to use an array you have to declare the
> size up front.  Java has a Vector class which is an array of objects
> which grows as you add things to it.

The comment about "most of the time" isn't really true for Python,
where the default tends to be dynamic more than static structure
declarations.  Heck, even a class in Python isn't really a fixed
definition, but is completely malleable at run-time.

> "Just curiousity on my part really, but if you are serious about using
> Python productively, you probably need to answer that.  In Java, for
> instance, if I want an array of String I say "String tmp[]=new
> String[5]" and I have an array of Strings with 5 slots.  If I didn't
> know how many Strings I was going to have though, I could say "Vector
> tmp=new Vector()" then every time I wanted to add a String, say "String
> tmpvalue" I could say "tmp.addElement(tmpvalue)".  Then, I could say
> "tmp.size()" to see how many elements were in the Vector, and I can even
> to a "tmp.elementAt(int x)" to retrieve a value.  So, I think the
> terminology would be that Java supports dynamic arrays of objects.  I
> was wondering if Python had the equivalent."

One of the fundamental Python types - a list - works this way.  You
don't define the overall size of a list, can append to it at will (the
.append method) in addition to inserting entries at arbitrary
locations (the .insert method) among other methods, can query the
length with len(), and a list is a container of a heterogenous set of
objects, so you can add anything you want to it, including other
lists.  For retrieval, the objects are just indexed like an array
([#]), and you can also extract "slices" of the list (e.g., a range of
entries) as another list.  It's one of a general class of types called
sequences.

If you need keyed access to a heterogenous set of objects, you would
use a dictionary type (a class of types called mappings), which would
let you insert and retrieve the information based on a key, which
itself can be a fairly broad range of object types.

You might point the person who originally sourced the query to take a
quick glance at the first few sections of chapter 2 of the library
reference (Built-in Types, Exceptions and Functions) - it's short, and
might pique their interest :-)

--
-- David
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