Converts bytes, unicode, and C char arrays to bytes.

    Unicode strings are encoded to UTF-8.

def to_bytes(value):
    """Converts bytes, unicode, and C char arrays to bytes.

    Unicode strings are encoded to UTF-8.
    """
    if isinstance(value, text_type):
        return value.encode('utf-8')
    elif isinstance(value, ffi.CData):
        return ffi.string(value)
    elif isinstance(value, binary_type):
        return value
    else:
        raise ValueError('Value must be text, bytes, or char[]')