The dictionary and collection of Python

Learn about the dictionaries and collections that go into Python.

Review the collection first.

In Python, the collection is represented by set. Curly braces and set () can be used to create collections.

or create an empty collection first

You cannot use s={} to create a collection that creates an empty collection using Set ().

The collection is unordered and non-repeating, so the elements that are duplicated when the collection is created are removed.

Basic operations of the collection:

Hand &

and |

Poor

Symmetrical difference ^

As an example:

Set s1={1,2,3,4}, set s2={2,3,5}

The

>>> s1={1,2,3,4}>>> s2={2,3,5}>>> s1|s2{1, 2, 3, 4, 5}>>> s1&s2{2, 3}>> > S1-s2{1, 4}>>> s1^s2{1, 4, 5}.

Dictionary:

Dictionaries can be called associative stores, dictionaries are indexed by keys, and keys are immutable types, usually with strings and numbers as keys. A dictionary can be thought of as a collection of keys: Values .

The key must be unique in a dictionary. Create an empty dictionary: {}

A common way to create a dictionary:

>>> dic={"A": 1, "B": 2, "C":3}>>> dic{' C ': 3, ' B ': 2, ' a ': 1}>>> dic["a"]1>>> dic["B"] 2>>> dic["C"]3

Returns a list of key values using list (Dic.keys ())

>>> list (Dic.keys ()) [' C ', ' B ', ' a ']

Of course, you can also use Dict () to create a dictionary.

>>> dict ([' Sape ', 4139), (' Guido ', 4127), (' Jack ', 4098)]) {' Sape ': 4139, ' Guido ': 4127, ' Jack ': 4098}

　　

The dictionary and collection of Python