Dictionary operations in Python

Dictionary: Dict

Dictionaries are also referred to in other programming languages as associative arrays or hash lists through keys for element access: unordered collections, mutable type containers, variable length, heterogeneous, nested representations: Phonebook = {' Alice ': ' 1234 ', ' Beth ': ' 9102 ',...} A dictionary consists of a key and a corresponding value, a key-value pair called an item. In the previous example, the key is the first name and the value is the phone number. Each key is separated from its value with a colon (:), the item is separated by a comma, and the entire dictionary is enclosed in curly braces {}.dict = {} Defines an empty dictionary dict = {key1:value1,key2:value2,...} Note: In dictionaries (and other mapping types), keys must be unique, if the key conflicts, the last one (can be a hash object can be used as a key, because in the lookup is the key made a hash table to find, so the speed is very fast, the dictionary itself is not a hash, not the dictionary itself when the key, When a dictionary is nested in a dictionary, the internal dictionary can be used as a value instead of as a value, and the values in the dictionary do not need to be. Dict = {' x ': 123, ' Y ': 234, ' Z ': 456}print (dict[' x ']) 123len: Returns the number of elements in the dictionary >>> dict = {' A ': 1, ' B ': 2, ' C ':3}>> > Print (len (dict)) 3 Dictionary copy: dict.copy () deep Copy dict1 = Dict.copy () >>> Dict1 = {' x ': 1, ' Y ': 2, ' Z ':3}>>> Dict2 = Dict1 (shallow copy) >>> ID (DICT1) 140166806717496>>> ID (dict2) 140166806717496>>> dict3 = Dict1.copy () (Deep copy, memory location change) >>> ID (dict3) 140166805562568dict.get (Gets the value of the corresponding key) >>> dict = {' x ': 1, ' Y ': 2, ' Z ':3}>>> dict.get (' x ') 1>>> dict.get (' y ') 2>>> dict.get (' z ') 3>>> >>> Dict.get (' h ') (Get'sBenefits without this element will not throw an exception) >>> Dict.items (the key value in D, the way the dictionary is converted to a tuple list) Note: Each item is split into a tuple that is grouped together to form a list >>> dict = {' X ': 1, ' Y ':2}>>> dict.items () dict_items ([' X ', ' 1 '), (' Y ', 2)]) variable unpacking (both sides to be consistent) >>> Dict = {' x ': 1, ' Y ':2}> >> t1,t2 = Dict.items () >>> print (T1) (' x ', 1) >>> print (T2) (' Y ', 2) >>&gt ; Dict.keys (return key list) >>> Dict = {' x ': 1, ' Y ': 2, ' Z ':3}>>> Dict.keys () Dict_keys ([' X ', ' y ', ' z ']) dict.value ( return value list) >>> dict = {' x ': 1, ' Y ': 2, ' Z ':3}>>> dict.values () dict_values ([1, 2, 3]) Dict.pop (Popup specified key) > >> dict = {' x ': 1, ' Y ': 2, ' Z ':3}>>> dict.pop (' x ') 1>>> print (dict) {' Y ': 2, ' Z ': 3}>>> Dict.popitem (Random popup entry) >>> dict = {' A ': 1, ' B ': 2, ' C ': 3, ' d ': 4, ' E ': 5, ' F ': 6, ' G ':7}>>> dict.popitem (' G ') , 7) >>> Dict.popitem (' F ', 6) >>> Dict.popitem (' E ', 5) >>> Dict.popitem () (' d ', 4) >> > dict.update (Merge a dictionary into the current dictionary) Note: Duplicate keys will be overwritten by the update () method for using the DICT2 The key value pair is added to dict this method does not return any content. >>> Dict1 = {' A ': 1, ' B ':2}>>> dict2 = {' x ': 666, ' A ':888}>>> dict1.update (dict2) >>> Print (Dict1) {' A ': 888, ' B ': 2, ' x ': 666}>>> dict.clear () empty dictionary >>> dict1 = {' A ': 888, ' B ': 2, ' x ': 666}&gt ;>> dict1.clear () >>> dict1{}

Dictionary operations in Python