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This article introduces the relevant knowledge of "what is the concept and function of Python dictionary and how to create and use it". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

A dictionary is an unordered variable sequence of "key-value pairs". Each element in the dictionary is a "key-value pair", including "key object" and "value object".

You can quickly get, delete and update the corresponding "value object" through the "key object". In the list, we find the corresponding object through the "subscript number".

Find the corresponding "value object" through the "key object" in the dictionary. "key" is any immutable data, such as integers, floating-point numbers, strings, tuples.

However: lists, dictionaries, collections, such as mutable objects, can not be used as "keys", and "keys" can not be repeated.

The value can be arbitrary data and can be repeated.

A typical dictionary is defined: a = {'name':'jeames','age':18,'job':'programmer'}

1 the creation of a dictionary

1.1 We can create dictionary objects through {}, dict ()

> a = {'name':'jeames','age':18,'job':'programmer'} > b = dict (name='jeames',age=18,job='programmer') > a = dict ([("name", "jeames"), ("age", 18)]) > c = {} # empty dictionary object > d = dict () # empty dictionary object

1.2 create a dictionary object through zip ()

> k = ['name','age','job'] > v = [' jeames',18,'techer'] > d = dict (zip (kcopv)) > d {'name':' jeames', 'age': 18' job': 'techer'}

1.3 create a dictionary with an empty value through fromkeys

> a = dict.fromkeys (['name','age','job']) > > a {' name': None, 'age': None,' job': None}

2 access to dictionary elements

To test various access methods, we set a dictionary object here: a = {'name':'jeames','age':18,'job':'programmer'}

2.1 obtain "value" through [key]

If the key does not exist, an exception is thrown

> a = {'name':'jeames','age':18,'job':'programmer'} > a [' name'] 'jeames' > a [' age'] 18 > > a ['sex'] Traceback (most recent call last): File ", line 1, in a [' sex'] KeyError: 'sex'

2.2. Get the "value" through the get () method, which is recommended

The advantage is: the specified key does not exist, return None; can also set the default returned object when the specified key does not exist, it is recommended to use get () to get the "value object".

> a.get ('name')' gaoqi' > a.get ('sex') > a.get (' sex',' a man')'a man'

2.3 list all key-value pairs

> a.items () dict_items ([('name',' gaoqi'), ('age', 18), (' job', 'programmer')])

2.4 list all keys, list all values

> a.keys () dict_keys (['name',' age', 'job']) > a.values () dict_values ([' jeames', 18, 'programmer'])

3 Dictionary elements add / delete

Add "key-value pair" to the dictionary. If the key already exists, the old key-value pair is overwritten; if the key does not exist, a new key-value pair is added

> a = {'name':'jeames','age':18,'job':'programmer'} > a [' address'] = 'Hefei' > > a ['age'] = 16 > a {' name':' gaoqi', 'age': 16,' job':'programmer', 'address':' Hefei'}

To delete elements in the dictionary, you can use the del () method

Or clear () deletes all key-value pairs; pop () deletes the specified key-value pair and returns the corresponding "value object"

> a = {'name':'jeames','age':18,'job':'programmer'} > del (a [' name']) > > a {'age':18,'job':'programmer'} > b = a.pop (' age') > b18 "what is the concept and function of the Python dictionary and how to create and use it" is introduced here, thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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