Python dictionaries, collections

A dictionary is a mutable container model and can store any type of object

Characteristics:

The dictionary is unordered, it cannot be accessed by an offset, only by a key.

internal no order, through the key to read the content, can be nested, merge, convenient for us to organize a variety of data structures, and can modify the contents inside, belong to the mutable type.

The keys that make up the dictionary must be immutable data types, such as numbers, strings, tuples, and so on, and mutable objects such as lists cannot be keys

1. Definition of Dictionary

A = {' 1 ': ' A ', ' 2 ': ' B ', ' 3 ': ' C '}
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A = Dict (1= ' A ', 2= ' B ', 3= ' C ')

2. Insert Content

A[4] = ' d '
The result is: {' 1 ': ' A ', ' 2 ': ' B ', ' 3 ': ' C ', ' 4 ': ' d '}

3. Modify the Content

a[' 1 '] = ' q '
The result is: {' 1 ': ' Q ', ' 2 ': ' B ', ' 3 ': ' C ', ' 4 ': ' d '}

4. Delete Content

Del (a[' 1 '])

The result is: {' 2 ': ' B ', ' 3 ': ' C ', ' 4 ': ' d '}

Common methods:

Dict.keys () View dict keys

Divt.values () View all the values in the Dict

Dict.items ()

Dict.clear () Delete all the elements in the dictionary

Dict.pop ()

Dict.get (' key ') gets the value of a key from the dictionary

Dict.has_key (' key ')

Collection

The collection is divided into mutable set (set) and immutable set (Frozenset)

Set hash, Frozenset non-hash (infrequently used)

Set is a non-repeating set of elements that support Union (union), intersection (intersection), difference (differential set), and sysmmetric difference (symmetric difference sets), and other mathematical operations

1. Definition set (SET)

A = set (' Aasdfsdfa ')
The result is: {' A ', ' d ', ' f ', ' s '}

2. Seeking Union (Union)

A = set (' abc ') b = Set (' BCD ') c = a|b
The result is: {' A ', ' B ', ' C ', ' d '}

3. Seeking intersection (intersection)

c = a&b
The result is: {' B ', ' C '}

4, Seek difference (difference set)

c = A-B
The result is: {' A '}

Common methods:

Set.add (obj) adds a value

Set1.difference (Set2) Seeking difference set

Set1.union (Set2) seeking union

Set1.intersection (Set2) to seek the intersection

Set.remove (obj) removing obj

Set.clear ()

Set.pop ()

Python dictionaries, collections