Seq

In Biopython, sequences are usually held as Seq objects, which hold the sequence string and an associated alphabet. There is a whole chapter in the Tutorial (PDF) on the Seq object.

If you need to store additional information like a sequence identifer or name, or even more details like a description or annotation, then we use a SeqRecord object instead. These are the sequence records used by the SeqIO module for reading and writing sequence files.