Section 2.1.7.9 of the library reference explains that file objects support a fileno method. Is that a mandatory operation on file-like objects (e.g. StringIO)? If so, how should it be implemented? If not, shouldn't the documentation declare it optional?

The same question for documented attributes: closed, mode, name, softspace: need file-like objects to support them?

fileno() (and isatty()) is OS specific and only works if there *is* an underlying file number. It should not be implemented (not even as raising an exception) if it isn't there. Support for softspace is needed when you expect to be printing to a file. The others are implementation details of the built-in file object, but would be nice to have if they can be implemented; code that requires them is not fully supportive of file-like objects. Note that this (and other, similar issues) is all because Python doesn't have a standard class hierarchy. I expect that we'll fix all this in Python 3000. Until then, I guess we have to muddle forth... BTW, did you check in test cases for all the methods you fixed? --Guido van Rossum (home page: http://www.pythonlabs.com/~guido/)