Python Basic Tutorial Note 14: Dictionary (Dictionary)

Pythondictionary (Dictionary)

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

Each key value of the dictionary is key=>value with a colon : Split, with a comma, split between each key-value pair, and the entire dictionary is enclosed in curly braces {}, as shown in the following format:

D = {key1:value1, key2:value2}

The key is generally unique, and the value does not need to be unique if the last key value pair is repeated instead of the previous one.

>>>dict = {'a': 1,'b': 2,'b':'3'};>>> dict['b']'3'>>>dict{'a': 1,'b':'3'}

The value can take any data type, but the key must be immutable, such as a string, a number, or a tuple.

A simple Dictionary instance:

Dict = {'Alice'2341'Beth ' '9102'Cecil'3258' }

You can also create a dictionary like this:

' ABC ': 456'abc': 123, 98.6:37};

Accessing values in the dictionary

Put the corresponding key into the familiar square brackets, the following example:

Dict = {'Name':'Zara',' Age': 7,'Class':' First'}; Print "dict[' Name ']:", dict['Name'];Print "dict[' age ']:", dict[' Age'];

Results:

dict['Name':  zaradict['age':  7

If the data is accessed using a key that is not in the dictionary, the output error is as follows:

Dict = {'Name''Zara'' age '  Class'First'print ' ", dict['Alice'];  

Results:

dict['Alice': Traceback (most recent call last)  :"test.py  " in <module>    print"", dict['   Alice ' Alice '

Modify Dictionary

The way to add new content to a dictionary is to add a new key/value pair, modify or delete an existing key/value pair as follows:

Dict = {'Name':'Zara',' Age': 7,'Class':' First'}; dict[' Age'] = 8;#Update Existing entrydict['School'] ="DPS School";#ADD new Entry  Print "dict[' age ']:", dict[' Age'];Print "dict[' School ']:", dict['School'];

Results:

dict['age ':  8dict['School'] :  DPS School

Delete a dictionary element

The ability to delete a single element also clears the dictionary, emptying only one operation.

Show Delete a dictionary with the Del command, as in the following example:

Dict = {'Name':'Zara',' Age': 7,'Class':' First'}; deldict['Name'];#Delete key is ' Name ' entryDict.clear ();#Empty dictionary all entriesdelDict;#Delete Dictionary Print "dict[' age ']:", dict[' Age'];Print "dict[' School ']:", dict['School'];

However, this throws an exception because the dictionary no longer exists after Del:

dict['age ']:traceback (most recent call last):  "test.py "  in <module>    print"", dict['age  ' type'is unsubscriptable

Properties of Dictionary Keys

A dictionary value can take any Python object without restriction, either as a standard object or as a user-defined one, but not a key.

Two important points to keep in mind:

1) The same key is not allowed to appear two times. When created, if the same key is assigned a value of two times , the latter value is remembered, as in the following example:

Dict = {'Name''Zara'' age '  Name'manni'print ", dict['Name'];  

Results:

dict['Name']:  Manni

2) The key must be immutable, so it can be used as a number, string or tuple, so the list is not, the following example:

Dict = {['Name''Zara'age' : 7print"", dict['Name' ];

Results:

Traceback (most recent):   " test.py "  in <module>    = {['Name''Zara'  'age': 7}; Typeerror:list Objects is unhashable

Python Basic Tutorial Note 14: Dictionary (Dictionary)