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Note: 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 to MutableString).
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 MutableString.
The UserString module defines the following classes:
-
| class UserString( |
[sequence]) |
- 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.
-
| class MutableString( |
[sequence]) |
- 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 attribute:
- data
- A real Python string or Unicode object used to store the content of the UserString class.
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