code: def replace(input, **pars):
      
      pixvalue = pars.get('pixvalue', np.nan)
      if pixvalue is None: pixvalue = np.nan # insure that None == np.nan
  
      newvalue = pars.get('newvalue', 0.0)
      ext = pars.get('ext',None)
      if ext in ['',' ','None',None]:
          ext = None
  
      files = parseinput.parseinput(input)[0]
  
      for f in files:
          fimg = fits.open(f, mode='update', memmap=False)
  
          if ext is None:
              # replace pixels in ALL extensions
              extn = [i for i in fimg]
          else:
              if type(ext) == type([]):
                  extn = [fimg[e] for e in ext]
              else:
                  extn = [fimg[ext]]
  
          for e in extn:
              if e.data is not None and e.is_image: # ignore empty Primary HDUs
                  print("Converting {}[{},{}] value of {} to {}".format(
                          f,e.name,e.ver,pixvalue,newvalue))
                  if np.isnan(pixvalue):
                      e.data[np.isnan(e.data)] = newvalue
                  else:
                      e.data[np.where(e.data == pixvalue)] = newvalue
  
          fimg.close()
docs: Replace pixels in `input` that have a value of `pixvalue`
          with a value given by `newvalue`.