'Constructor.
Args:
filename: File\'s name as string.
content_type: File\'s content type. Value from FileContentType.ContentType
enum.'

def __init__(self, filename, mode, content_type, exclusive_lock):

    self._filename = filename
    self._closed = False
    self._content_type = content_type
    self._mode = mode
    self._exclusive_lock = exclusive_lock
    self._offset = 0
    self._open()
