Comment 6 for bug 218128

from bzrlib.textfile:

def text_file(input):
    """Produce a file iterator that is guaranteed to be text, without seeking.
    BinaryFile is raised if the file contains a NUL in the first 1024 bytes.
    """
    first_chunk = input.read(1024)
    if '\x00' in first_chunk:
        raise BinaryFile()
    return IterableFile(chain((first_chunk,), file_iterator(input)))