The docs for pickle, in python 2, say that the default pickle protocol, 0, produces ASCII. In the python 3 docs, this has changed to "human-readable". While the pickle output with protocol 0 loads fine in python2, it is definitely not human-readable, as it is not valid ASCII and contains every possible byte.

To see a simple example, run this in both python 2 and 3

import pickle
a = bytearray(range(255)) #bytes containing 0..255
b = bytes(a)
c = pickle.dumps(b,protocol=0)
print(c)#human readable in 2, not in 3
c.decode('ascii')#throws in 3, not in 2