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Tarfile would benefit from exposing custom compressors. At the moment the only way to use something that is not gzip/bzip/lzma is to separate the archiving and compression steps.
A possible approach is to pass a custom compression function to `tarfile.TarFile.open`. However the current interface is not clean enough to be exposed. I have made a very conservative change via a pull request on GitHub, see https://github.com/python/cpython/pull/2734 . Some additional considerations can be found there.
A further step could require a simplified interface that only involves file name, file-like object and compression level, and returns a file-like object to read the compressed data from. For example:
def my_compressor(name, fileobj=None, compresslevel=9):
 # compression happens here
 return filelike_object
This further step is not captured in the pull request, but I can iterate and update the diff.

Adding lars.gustaebel who is listed as maintainer for tarfile.

Adding serhiy.storchaka who recently made changes to tarfile.

You can pass a custom file object that implements a custom compression to the TarFile constructor. I don't see a need in other way.

The documentation should be updated to suggest that a custom file-like object can be passed to have custom compressors then.
However this sounds very hacky and definitely not a feature that can be easily passed to the user. Hence the reason for a cleaner, explicitly advertised interface.