According to the Python docs:
class zipfile.ZipFile(file[, mode[, compression[, allowZip64]]])
Open a ZIP file, where file can be either a path to a file (a string) or a file-like object.
So, to open the file in memory, just create a file-like object (perhaps using BytesIO).
file_like_object = io.BytesIO(my_zip_data)
zipfile_ob = zipfile.ZipFile(file_like_object)