GNU Info

(python2.1-lib.info)UserList

---

Next: UserString Prev: UserDict Up: Python Runtime Services

---

Enter node , (file) or (file)node

Class wrapper for list objects
==============================

Class wrapper for list objects.

This module defines a class that acts as a wrapper around list objects.
It is a useful base class for your own list-like classes, which can
inherit from them and override existing methods or add new ones.  In
this way one can add new behaviors to lists.

The `UserList' module defines the `UserList' class:

`UserList([list])'
     Class that simulates a list.  The instance's contents are kept in
     a regular list, which is accessible via the `data' attribute of
     `UserList' instances.  The instance's contents are initially set
     to a copy of LIST, defaulting to the empty list `[]'.  LIST can be
     either a regular Python list, or an instance of `UserList' (or a
     subclass).

In addition to supporting the methods and operations of mutable
sequences (see section Note: Sequence Types), `UserList' instances
provide the following attribute:

`data'
     A real Python list object used to store the contents of the
     `UserList' class.

*Subclassing requirements:* Subclasses of `UserList' are expect to
offer a constructor which can be called with either no arguments or one
argument.  List operations which return a new sequence attempt to
create an instance of the actual implementation class.  To do so, it
assumes that the constructor can be called with a single parameter,
which is a sequence object used as a data source.

If a derived class does not wish to comply with this requirement, all
of the special methods supported by this class will need to be
overridden; please consult the sources for information about the
methods which need to be provided in that case.

_Changed in Python version 2.0_