A dictionary of Python data types

First, what is a dictionary

1. The dictionary is the only type of mapping in Python, consisting of key-value pairs enclosed in {},

2. The key of the element in the dictionary: must be a hash immutable data type that can be used as a key in the dictionary

3. The value of the element in the dictionary: there is no limit to what data type can be

Second, the dictionary additions and deletions to search

1. Increase

Dic[key]=value add directly (Key:value) (this method can also be used to modify the dictionary)

Dic.setdefault (Key,value) If the key is already present in the dictionary, do nothing, otherwise add (Key:value)

Do not enter the value parameter to query, if not the key will return none

2. By deleting

Pop (key) has a return value that returns the value corresponding to key

Del Dic[key] Delete key and his corresponding value (del dic = delete entire dictionary, again query cannot find this dictionary)

Popitem () random Delete, latest Python version delete last key value pair

Clear () Empty dictionary dictionary into empty Dictionary {}

3. Change

Dic[key] = value forced modification

Dic.update (dictionary) The old Dictionary before the new dictionary is overwritten

4. Enquiry

Dic.get (Key)

For loop

Dic[key]

SetDefault (mentioned above)

Third, the special operation of the dictionary

Dic.keys gets all the keys in the dictionary stored in a high-copy list

Dic.values gets all the values in the dictionary stored in a high-copy list

Dic.items gets all the key-value pairs in the dictionary in a high-copy list

Iv. Deconstruction

A, B = (a=1,b=2)

A, B = "a" (a=1,b=2)

V. Nesting of dictionaries

Similar to the list of nesting!

　　

A dictionary of Python data types