code: def fn_getma(fn, bnum=1, return_ds=False):
      
      #Add check for filename existence
      ds = fn_getds(fn)
      out = ds_getma(ds, bnum=bnum)
      if return_ds:
          out = (out, ds)
      return out
docs: Get masked array from input filename
  
      Parameters
      ----------
      fn : str
          Input filename string
      bnum : int, optional
          Band number
      
      Returns
      -------
      np.ma.array    
          Masked array containing raster values