How to construct a TarFile object in memory from byte buffer in Python 3?

BytesIO() from IO module does exactly what you need.

import tarfile, io
byte_array = client.read_bytes()
file_like_object = io.BytesIO(byte_array)
tar = tarfile.open(fileobj=file_like_object)
# use "tar" as a regular TarFile object
for member in tar.getmembers():
    f = tar.extractfile(member)
    print(f)