support indexing by keyetc ' including the python byte strings and unicode strings mentioned at the start of this under the general "stringslabel here (see sets are something of category unto themselves (they don' map keys to values and are not positionally ordered sequences)and we haven' yet explored mappings on our in-depth tour (we will in the next howevermany of the other types we will encounter will be similar to numbers and strings for examplefor any sequence objects and yx makes new sequence object with the contents of both operands makes new sequence object with copies of the sequence operand in other wordsthese operations work the same way on any kind of sequenceincluding stringsliststuplesand some user-defined object types the only difference is that the new result object you get back is of the same type as the operands and --if you concatenate listsyou get back new listnot string indexingslicingand other sequence operations work the same on all sequencestoothe type of the objects being processed tells python which flavor of the task to perform mutable types can be changed in place the immutable classification is an important constraint to be aware ofyet it tends to trip up new users if an object type is immutableyou cannot change its value in placepython raises an error if you try insteadyou must run code to make new object containing the new value the major core types in python break down as followsimmutables (numbersstringstuplesfrozensetsnone of the object types in the immutable category support in-place changesthough we can always run expressions to make new objects and assign their results to variables as needed mutables (listsdictionariessetsbytearrayconverselythe mutable types can always be changed in place with operations that do not create new objects although such objects can be copiedin-place changes support direct modification generallyimmutable types give some degree of integrity by guaranteeing that an object won' be changed by another part of program for refresher on why this matterssee the discussion of shared object references in to see how listsdictionariesand tuples participate in type categorieswe need to move ahead to the next string fundamentals