Python3 dictionary Dict (13), python3 dictionary dict

Python3 dictionary Dict (13), python3 dictionary dict

Python has built-in dictionaries: dict support. dict stands for dictionary and is also called map in other languages. It is stored with key-value (key-value) and has extremely fast search speed.

Dictionary is another variable container model that can store any type of objects.

Each key-value (key => value) pair of the dictionary uses the colon (:), And each pair is separated by a comma (,The entire dictionary is included in curly brackets ({})The format is as follows:

d = {key1 : value1, key2 : value2 }

The key must be unique, but the value is not required..

Values can be of any data type, but keys must be unchangeable, such as strings, numbers, or tuples.

A simple dictionary example:

1 dict = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}

You can also create a dictionary as follows:

1 dict1 = { 'abc': 456 };2 dict2 = { 'abc': 123, 98.6: 37 };

Value in the access dictionary

Place the corresponding keys in the familiar square brackets, as shown in the following example:

1 #!/usr/bin/python32 3 dict = {'Name': 'Runoob', 'Age': 7, 'Class': 'First'}4 5 print ("dict['Name']: ", dict['Name'])6 print ("dict['Age']: ", dict['Age'])

Output result of the above instance:

1 dict['Name']:  Runoob2 dict['Age']:  7

If you use a key that is not in the dictionary to access data, an error is returned.

1 >>> info = {'stu1102': 'longze Luola ', 'stu1103 ': 'xiaoze Maliya '} 2 >>> 3 >>> "stu1102" in info # standard usage 4 True 5 >>> info. get ("stu1102") # obtain 6 'longze Luola '7> info ["stu1102"] # Same as above, but let's see the following 8 'longze Luola '9 >>> info ["stu1105"] # If a key does not exist, an error is returned. get does not, if not, only None10 Traceback (most recent call last): 11 File "<stdin>", line 1, in <module> 12 KeyError: 'stu1105' is returned'

Modify dictionary

You can add a new key/value pair to a dictionary to modify or delete an existing key/value pair as follows:

1 #! /Usr/bin/python3 2 3 dict = {'name': 'runoob', 'age': 7, 'class ': 'first'} 4 5 dict ['age'] = 8; # update Age 6 dict ['school '] = "cainiao tutorial" # add information 7 8 9 print ("dict ['age']:", dict ['age']) 10 print ("dict ['school ']:", dict ['school'])

Output result of the above instance:

1 dict ['age']: 82 dict ['school ']: cainiao tutorial

Delete dictionary elements

Only one operation is required to delete a single element and clear the dictionary.

The following example shows how to delete a dictionary using the del command:

1 #! /Usr/bin/python3 2 3 dict = {'name': 'runoob', 'age': 7, 'class ': 'first'} 4 5 del dict ['name'] # Delete the 'name' 6 dict. clear () # Delete dictionary 7 del dict # Delete dictionary 8 9 print ("dict ['age']:", dict ['age']) 10 print ("dict ['school ']:", dict ['school'])

However, this causes an exception because the dictionary does not exist after del is executed:

1 Traceback (most recent call last):2   File "test.py", line 9, in <module>3     print ("dict['Age']: ", dict['Age'])4 TypeError: 'type' object is not subscriptable

1 >>> info 2 {'stu1102': 'longze Luola ', 'stu1103': 'xiaoze Maliya', 'stu1101': 'lan'} 3 >>> info. pop ("stu1101") # standard Delete posture 4 'ran' 5> info 6 {'stu1102': 'longze Luola ', 'stu1103 ': 'xiaoze Maliya '} 7 >>> del info ['stu1103'] # change the posture to delete 8 >>> info 9 {'stu1102 ': 'longze Luola '} 10 >>> 11 >>>> 12 >>>>13 >>> info = {'stu1102': 'longze Luola', 'stu1103 ': 'xiaoze Maliya '} 14 >>> info15 {'stu1102': 'longze Luola', 'stu1103': 'xiaoze Maliya '} # Delete randomly 16 >>> info. popitem () 17 ('stu1102', 'longze Luola ') 18 >>> info19 {'stu1103': 'xiaoze Maliya '}

Dictionary key features

The dictionary value can be any python object, either a standard object or a user-defined object, but the key cannot.

There are two important points to remember:

1) the same key cannot appear twice. If the same key is assigned twice during creation, the last value will be remembered as follows:

1 #! /Usr/bin/python32 3 dict = {'name': 'runoob', 'age': 7, 'name ': 'cainiao '} 4 5 print ("dict ['name']:", dict ['name'])

Output result of the above instance:

1 dict ['name']: cainiao

2) The key must be unchangeable. Therefore, you can use numbers, strings, or tuples, but not lists. For example:

1 #!/usr/bin/python32 3 dict = {['Name']: 'Runoob', 'Age': 7}4 5 print ("dict['Name']: ", dict['Name'])

Output result of the above instance:

1 Traceback (most recent call last):2   File "test.py", line 3, in <module>3     dict = {['Name']: 'Runoob', 'Age': 7}4 TypeError: unhashable type: 'list'

Circular dictionary method:

# Method 1for key in info: print (key, info [key]) # method 2for k, v in info. items (): # convert dict to list first. print (k, v) is not used when the data is large)

1 dic = {"name": "lhm", "age": 33, "address": "wuhan", "job": "coding"}2 for i in dic:3     print(i, dic[i])4 print("-------------------------------")5 for a, b in dic.items():6     print(a, b)

The result is as follows:

1 job coding2 name lhm3 address wuhan4 age 335 -------------------------------6 job coding7 name lhm8 address wuhan9 age 33

Dictionary built-in functions & Methods

The Python dictionary contains the following built-in functions:

The Python dictionary contains the following built-in methods:

Serial number	Functions and descriptions
1	Radiansdict. clear () Delete all elements in the dictionary
2	Radiansdict. copy () Returns the shortest copy of a dictionary.
3	Radiansdict. fromkeys () Create a new dictionary and use the elements in sequence seq as the dictionary key. val is the initial value corresponding to all the keys in the dictionary.
4	Radiansdict. get (key, default = None) Returns the value of the specified key. If the value is not in the dictionary, the default value is returned.
5	Key in dict If the key returns true in the dictionary dict, otherwise false is returned.
6	Radiansdict. items () Returns a list of traversal (Key, value) tuples.
7	Radiansdict. keys () Returns all keys of a dictionary in a list.
8	Radiansdict. setdefault (key, default = None) Similar to get (), but if the key does not exist in the dictionary, a key is added and the value is set to default.
9	Radiansdict. update (dict2) Update the dictionary dict2 key/value pairs to dict.
10	Radiansdict. values () Returns all values in the dictionary as a list.
11	Pop (key [, default]) Delete the value corresponding to the specified key in the dictionary. The returned value is the deleted Value. The key value must be given. Otherwise, the default value is returned.
12	Popitem () Returns and deletes a pair of keys and values in the dictionary randomly (generally, the end pair is deleted ).