This UserString class from this module is available for
backward compatibility only. If you are writing code that does not
need to work with versions of Python earlier than Python 2.2, please
consider subclassing directly from the built-in str type
instead of using UserString (there is no built-in equivalent
This module defines a class that acts as a wrapper around string
objects. It is a useful base class for your own string-like classes,
which can inherit from them and override existing methods or add new
ones. In this way one can add new behaviors to strings.
It should be noted that these classes are highly inefficient compared
to real string or Unicode objects; this is especially the case for
The UserString module defines the following classes:
Class that simulates a string or a Unicode string
object. The instance's content is kept in a regular string or Unicode
string object, which is accessible via the data attribute of
UserString instances. The instance's contents are initially
set to a copy of sequence. sequence can be either a
regular Python string or Unicode string, an instance of
UserString (or a subclass) or an arbitrary sequence which can
be converted into a string using the built-in str() function.
This class is derived from the UserString above and redefines
strings to be mutable. Mutable strings can't be used as
dictionary keys, because dictionaries require immutable objects as
keys. The main intention of this class is to serve as an educational
example for inheritance and necessity to remove (override) the
__hash__() method in order to trap attempts to use a
mutable object as dictionary key, which would be otherwise very
error prone and hard to track down.
In addition to supporting the methods and operations of string and
Unicode objects (see section 2.3.6, ``String
Methods''), UserString instances provide the following
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A real Python string or Unicode object used to store the content of the