The data format used by pickle is Python-specific. This has the advantage that there are no restrictions imposed by external standards such as XDR(which can't represent pointer sharing); however it means that non-Python programs may not be able to reconstruct pickled Python objects.
By default, the pickle data format uses a printable ASCII representation. This is slightly more voluminous than a binary representation. The big advantage of using printable ASCII (and of some other characteristics of pickle's representation) is that for debugging or recovery purposes it is possible for a human to read the pickled file with a standard text editor.
A binary format, which is slightly more efficient, can be chosen by specifying a true value for the bin argument to the Pickler constructor or the dump() and dumps() functions.