Python in a Nutshell

The StringIO and cStringIO Modules

You can implement file-like objects by writing Python classes that supply the methods you need. If all you want is for data to reside in memory rather than on a file as seen by the operating system, you can use the StringIO or cStringIO module. The two modules are almost identical: each supplies a factory function to create in-memory file-like objects. The difference between them is that objects created by module StringIO are instances of class StringIO.StringIO. You may inherit from this class to create your own customized file-like objects, overriding the methods that you need to specialize. Objects created by module cStringIO, on the other hand, are instances of a special-purpose type, not of a class. Performance is much better when you can use cStringIO, but inheritance is not feasible. Furthermore, cStringIO does not support Unicode.

Each module supplies a factory function named StringIO that creates a file-like object fl.