code: def gzopen(cls, name, mode="r", fileobj=None, compresslevel=9, **kwargs):
          
          if len(mode) > 1 or mode not in "rw":
              raise ValueError("mode must be 'r' or 'w'")
  
          try:
              import gzip
              gzip.GzipFile
          except (ImportError, AttributeError):
              raise CompressionError("gzip module is not available")
  
          extfileobj = fileobj is not None
          try:
              fileobj = gzip.GzipFile(name, mode + "b", compresslevel, fileobj)
              t = cls.taropen(name, mode, fileobj, **kwargs)
          except IOError:
              if not extfileobj and fileobj is not None:
                  fileobj.close()
              if fileobj is None:
                  raise
              raise ReadError("not a gzip file")
          except:
              if not extfileobj and fileobj is not None:
                  fileobj.close()
              raise
          t._extfileobj = extfileobj
          return t
docs: Open gzip compressed tar archive name for reading or writing.
             Appending is not allowed.