readsb (Python) is a Python module containing a set of classes designed to open, read, and manipulate data files that are in SeaBASS file format. While many of Python's built-in functions may be used to read SeaBASS files, this module leverages Python libraries and tools to efficiently read, sort, mask, and return the contained data for easy use without errors or significant intervention. Using this function, data outputs will be returned as data structures containing the file's header information (metadata) as an array of strings, the file's comments as an array of strings, the file's missing data, above detection limit, and below detection limit values (if present), the file's variable and unit lists as an Ordered Dictionary indexed by variable name, and the file's data as an Ordered Dictionary indexed by variabile name. Additionally, optional arguments flags that may be toggled are mask_missing, mask_above_detection_limit, and mask_below_detection_limit (all set true by default), which remove the relevant header-defined fill values, replacing them with NaN.