Issue 1488634: tarfile.TarFile.open can might incorrectly raise ValueError (original) (raw)

tarfile.TarFile.open, if passed a fileobj argument for a valid plain tar or tar.gz file, might fail to open the file, and instead unexpectedly raise "ValueError: no support for external file objects".

"open" iterates over TarFile.OPEN_METH, which is a dictionary, to try find a method that works for a given file. If the internal, undefined, ordering of that dict returns the "bz2" key before the right one for a given file, and the fileobj argument is passed, TarFile will attempt to call bz2open with the fileobj method, which then raises "ValueError: no support for external file objects", which then is not caught.

The end result is that it's possible to pass a valid tar or tar.gz file to TarFile.open in the fileobj argument, but get a ValueError from bz2open instead of a TarFile object.