an expression bytearrays in recent pythons offer mutability for textbut they are not normal stringsand only apply directly to text if it' simple -bit kind ( ascii "sequenceis positionally ordered collection of objects stringslistsand tuples are all sequences in python they share common sequence operationssuch as indexingconcatenationand slicingbut also have type-specific method calls related term"iterable,means either physical sequenceor virtual one that produces its items on request the term "mappingdenotes an object that maps keys to associated values python' dictionary is the only mapping type in the core type set mappings do not maintain any left-to-right positional orderingthey support access to data stored by keyplus type-specific method calls "polymorphismmeans that the meaning of an operation (like +depends on the objects being operated on this turns out to be key idea (perhaps the key ideabehind using python well--not constraining code to specific types makes that code automatically applicable to many types introducing python object types