Python Collection Literal

Besides, scalar literal, Python also support collection literals. Literal collections is a collection of literals featured by the form of collections. The typical literal collections are list literal, tuple literal, dictionary literal, set literal, and frozenset literal.

Features of Python Collection Literal

LiteralElementArrangementMutabilityDuplicate Member Example ListitemOrderedMutableAllow [], [5,6,8] TupleitemOrderedImmutableAllow (), (5,6,7) Dictionarykey-value UnorderedMutableNot Allow{}, {'x':5} SetitemUnorderedMutableNot Allow Set(), {85,6,7} FrozensetitemUnorderedImmutableNot Allowfrozenset(), frozenset({85,6,7})

List Literals

A list literal is a container used to contain a variable length sequence of Python objects. Elements of list can be Python objects of other types. Python objects in the list are ordered, changeable, and allowing duplicate members. A list lteral is enclosed by a pair of square brackets with elements in the list are separated by commas ,. An extra comma at the end of the List will always be ignored. An empty List can be created by a pair of square brackets with no element inside.

Tuple Literals

A tuple literal is a container used to contain a fixed length sequence of Python objects. Elements of tuple can be Python objects of other types. Python objects in the tuple are ordered, unchangeable, and allowing duplicate members. A tuple is enclosed by a pair of parentheses with elements in the list are separated by commas ,. An extra comma at the end of the Tuple will always be ignored. However, when there is only one element in the tuple, a comma must be at the end in order to indicate that the element is a tuple. An empty Tuple can be created by a pair of parentheses with no element inside. Besides, a tuple can also be created without the using of a pair of parentheses.

Dictionary Literals

A dictionary literal is a container used to contain a variable length sequence of Python object pairs. Elements of dictionary value can be Python objects of other types. Python object pairs in the dictionary are unordered, changeable, and not allowing duplicate members. The Python object pair of a dictionary is the key and value of the dictionary. A dictionary is enclosed by a pair of curly braces.

Set Literals

A set literal is a container used to contain a variable length sequence of Python objects. Elements of set can be Python objects of other types. Python objects in the set are unordered, changeable, and not allowing duplicate members. Elements of a set is updated by methods of set. A set is also enclosed by a pair of curly braces. But elements of a set are single independent Python objects instead of a pair of Python objects of the form key-value pair. Beside an empty set can only be created by function set() without any argument or with no element, since empty curly braces will create an empty dictionary in Python.

Frozenset Literals

A frozenset literal is a container used to contain a fixed length sequence of Python objects. Elements of frozenset can be Python objects of other types. Python objects in the frozenset are unordered, unchangeable, and not allowing duplicate members. A frozenset is always displayed as an immutable copy of an ordinaryl set. e.g. frozenset({85,6,7}). And a frozenset is always created by using function frozenset() to convert a collection into frozenset.

Source and Reference

• https://docs.python.org/3/reference/introduction.html
• https://docs.python.org/3/reference/lexical_analysis.html#literals
• https://docs.python.org/3/reference/expressions.html
• https://docs.python.org/2.0/ref/atom-literals.html
• https://docs.python.org/3/library/stdtypes.html#binary-sequence-types-bytes-bytearray-memoryview