Normally, when opening an existing non-TAR file, e.g., a file with random data, an exception is raised:

tarfile.open( "foo.txt" )

    ---------------------------------------------------------------------------
    ReadError                                 Traceback (most recent call last)
    <ipython-input-53-aa60172c3e3b> in <module>()
    ----> 1 f = tarfile.open( "notes.txt", ignore_zeros = False )

    /usr/lib/python3.7/tarfile.py in open(cls, name, mode, fileobj, bufsize, **kwargs)
       1576                         fileobj.seek(saved_pos)
       1577                     continue
    -> 1578             raise ReadError("file could not be opened successfully")
       1579 
       1580         elif ":" in mode:

    ReadError: file could not be opened successfully

However, when specifying ignore_zeros = True, this check against invalid data seems to be turned off. Note that it is >invalid< data not >zero< data and therefore should still raise an exception!

tarfile.open( "foo.txt", ignore_zeros = True )

Iterating over that opened tarfile also works without exception however nothing will be iterated over, i.e., it behaves like an empty TAR instead of like an invalid TAR.