collection data types another consequence of the immutability of frozen sets is that they meet the hashable criterion for set itemsso sets and frozen sets can contain frozen sets we will see more examples of set use in the next sectionand also in the examples section mapping types || mapping type is one that supports the membership operator (inand the size function (len())and is iterable mappings are collections of key-value items and provide methods for accessing items and their keys and values when iteratedunordered mapping types provide their items in an arbitrary order python provides two unordered mapping typesthe built-in dict type and the standard library' collections defaultdict type newordered mapping typecollections ordereddictwas introduced with python this is dictionary that has the same methods and properties ( the same apias the built-in dictbut stores its items in insertion order we will use the term dictionary to refer to any of these types when the difference doesn' matter hashable objects only hashable objects may be used as dictionary keysso immutable data types such as floatfrozensetintstrand tuple can be used as dictionary keysbut mutable types such as dictlistand set cannot on the other handeach key' associated value can be an object reference referring to an object of any typeincluding numbersstringslistssetsdictionariesfunctionsand so on dictionary types can be compared using the standard equality comparison operators (=and !=)with the comparisons being applied item by item (and recursively for nested items such as tuples or dictionaries inside dictionariescomparisons using the other comparison operators (=>are not supported since they don' make sense for unordered collections such as dictionaries dictionaries | dict is an unordered collection of zero or more key-value pairs whose keys are object references that refer to hashable objectsand whose values are object references referring to objects of any type dictionaries are mutableso we can easily add or remove itemsbut since they are unordered they have no notion of index position and so cannot be sliced or strided api stands for application programming interfacea generic term used to refer to the public methods and properties that classes provideand to the parameters and return values of functions and methods for examplepython' documentation documents the apis that python provides