Python Dictionary

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

Each key-value (key=>value) pair in the dictionary is separated by a 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 }

Keys must be unique, but values do not.

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

A simple dictionary example:

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

You can also create a dictionary like this:

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

Access the value in the dictionary

Put the corresponding key in the familiar square brackets, as in the following example:

#!/usr/ bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};

print "dict['Name']: ", dict['Name'];
print "dict['Age']: ", dict['Age'];

Output result of the above example:

dict['Name']: Zara
dict['Age']: 7

If you access data using keys that are not in the dictionary, the following error will be output:

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};

print "dict['Alice']: ", dict['Alice'];

The above example output result:

dict['Zara']:
Traceback (most recent call last):
File "test.py", line 4, in <module>
print "dict['Alice']: ", dict['Alice'];
KeyError: 'Alice'

Modify Dictionary

The way to add new content to the dictionary is to add new key/value pairs, modify or delete existing key/value pairs as follows:

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};

dict['Age'] = 8; # update existing entry
dict['School'] = "DPS School"; # Add new entry

print "dict['Age']: ", dict['Age'];
print "dict['School']: ", dict['School'];

Output result of the above example:

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

Delete dictionary elements

Can delete a single element or clear the dictionary , clearing only requires one operation.

To display and delete a dictionary, use the del command, as shown in the following example:

#!/usr/bin/python
# -*- coding: UTF-8 -*-

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};

del dict['Name']; # The delete key is' Name' entries
dict.clear(); # Clear all entries in the dictionary
del dict am ;
print "dict['School']: ", dict['School'];

But this will throw an exception because the dictionary no longer exists after using del:

dict['Age']:

Traceback (most recent call last):

File "test.py", line 8, in <module>
print "dict[' Age']: ", dict['Age'];
TypeError: 'type' object is unsubscriptable

##Note:

del() method will also be discussed later.

Characteristics of dictionary keys

Dictionary values can take any python object without restrictions, either standard objects or user-defined, but keys cannot.

Two important points to remember:

#1) The same key is not allowed to appear twice. If the same key is assigned twice during creation, the latter value will be remembered, as in the following example:

!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'};

print "dict['Name']: ", dict[' Name'];

Output result of the above example:

dict['Name']: Manni

2) The key must be immutable, so it can use numbers, strings or elements Group acts as a group, so using a list will not work. The following example:

#!/usr/bin/python

dict = {['Name']: 'Zara', 'Age ': 7};

print "dict['Name']: ", dict['Name'];

Output result of the above example:

Traceback (most recent call last):
File "test.py", line 3, in <module>
dict = {['Name']: 'Zara', 'Age': 7} ;
TypeError: list objects are unhashable

Dictionary built-in functions & methods

The Python dictionary contains the following built-in functions:

Serial number	Function and description
1	cmp(dict1, dict2) Compare two Dictionary element.
2	len(dict) Calculate the number of dictionary elements, that is, the total number of keys.
3	str(dict) Output the printable string representation of the dictionary.
4	type(variable) Returns the input variable type. If the variable is a dictionary, returns the dictionary type.

The Python dictionary contains the following built-in methods:

##radiansdict.has_key(key)6radiansdict.items()7radiansdict.keys()8radiansdict.setdefault(key , default=None)9radiansdict.update(dict2)10radiansdict.values()

Serial number	Function and description
1	radiansdict.clear() Delete all elements in the dictionary
2	radiansdict .copy() Returns a shallow copy of the dictionary
3	radiansdict.fromkeys() Creates a new dictionary to sequence the elements in seq Be the key of the dictionary, val is the initial value corresponding to all keys in the dictionary
4	radiansdict.get(key, default=None) Returns the specified key Value, if the value is not in the dictionary, return the default value
5	Returns true if the key is in the dictionary dict, otherwise returns false
	Returns a traversable (key, value) tuple array as a list
	Returns all the keys of a dictionary as a list
	Similar to get(), but if the key does not exist in the dictionary, the key will be added and the value will be set to default
	Update the key/value pairs of dictionary dict2 into dict
	Returns all values in the dictionary as a list

← Python tuple

Python date and time →

Python Dictionary

Access the value in the dictionary

Modify Dictionary

Delete dictionary elements

Dictionary built-in functions & methods

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