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Create a Python dictionary that returns a list of values for each key. The key can be whatever type you want.

Nội dung chính

    Create a dictionary first
    Method 1: Add new keys using the Subscript notation 
    Method 2: Add new keys using update()

    method 

    Method 3: Add new keys using the

    __setitem__ method

     Method 4: Add new keys using the ** operator 
    Method 5: Add new keys using the “in” operator and IF statements.
    Method 6: Add new keys using a for loop and enumerate() method
    Example 7: Add Multiple Items to a Python Dictionary with Zip
    How do you add a value to a key in Python?
    How do you assign a key to a dictionary in Python?
    How do you call a key in Python?
    How do I add a key value pair to a dictionary?

Design the dictionary so that it could be useful for something meaningful to you. Create least three different items in it. Invent the dictionary yourself. Do not copy the design or items from some other source.

Next consider the invert_dict function from Section 11.5 of your textbook.

# From Section 11.5 of:

# Downey, A. (2015).

Think Python: How to think like a computer scientist. Needham, Massachusetts: Green Tree Press.

def invert_dict(d):

inverse = dict()

for key in d:

val = d[key]

if val not in inverse:

inverse[val] = [key]

else:

inverse[val].append(key)

return inverse

my_dict =

    “Great Britain”: [“Bristol”,’Cambridge’,”Canterbury”],

    “France”: [“Paris”,’Marseille’,”Lyon”],

    “USA”: [“New York”,’California’,”Illinois”],

def invert(d):

    inverse = dict()

    for key in d:

        val = d[key]

        for item in val:

            if item not in inverse:

                inverse[item] = [key]

            else:

                inverse[item].append(key)

    return inverse 

print(‘Initial dictionary n’)

print(my_dict, ‘n’)

in_dict = invert(my_dict)

print(“Inverted dictionary n”)

print(in_dict)

Suppose there is a dictionary named exam_marks as given below.

exam_marks = ‘Cierra Vega’: 175, ‘Alden Cantrell’: 200, ‘Kierra Gentry’: 165, ‘Pierre Cox’: 190

Write a Python program that takes an input from the user and creates a new dictionary with only those elements from ‘exam_marks’ whose keys have values higher than the user input (inclusive).

===================================================================

Sample Input 1:

170

Sample Output 1:

‘Cierra Vega’: 175, ‘Alden Cantrell’: 200, ‘Pierre Cox’: 190

In this article, we will cover how to add a new Key to a Dictionary in Python. We will use 7 different methods to append new keys to a dictionary.

Dictionary in Python is an unordered collection of data values, used to store data values like a map, unlike other Data Types that hold

only a single value as an element, a Dictionary holds a key: value pair. Key-value is provided in the dictionary to make it more optimized. Each key-value pair in a Dictionary is separated by a colon: whereas each key is separated by a ‘comma’. The keys of a Dictionary must be unique and of immutable data types such as Strings, Integers, and tuples, but the key values can be repeated and be of any type. Let’s see how can we add new keys to a dictionary using different ways to a

dictionary.

Create a dictionary first

Python3

class my_dictionary(dict):

  def __init__(self):

    self = dict()

  def add(self, key, value):

    self[key] = value

dict_obj = my_dictionary()

dict_obj.add(1, ‘Geeks’)

dict_obj.add(2, ‘forGeeks’)

print(dict_obj)

Output:

1: ‘Geeks’, 2: ‘forGeeks’

Method 1: Add new keys using the Subscript notation 

This method will create a new keyvalue pair on a dictionary by assigning a value to that key. If the key doesn’t exist, it will be added and will point to that value. If the key exists, the current value it points to will be overwritten. 

Python3

dict =

‘key1’: ‘geeks’, ‘key2’: ‘fill_me’

print(“Current Dict is: “

  , dict)

dict[‘key2’] = ‘for’

dict[‘key3’] = ‘geeks’

print(“Updated Dict is:”

  , dict)

Output:

Current Dict is: ‘key1’: ‘geeks’, ‘key2’: ‘fill_me’

Updated Dict is: ‘key3’: ‘geeks’, ‘key1’: ‘geeks’, ‘key2’: ‘for’

Method 2: Add new keys using update()

method 

When we have to update/add a lot of key/values to the dictionary, the update() method is suitable. The update() method inserts the specified items into the dictionary.

Python3

dict = ‘key1’: ‘geeks’, ‘key2’: ‘for’

print(

  “Current Dict is:”

  , dict)

dict.update(‘key3’: ‘geeks’)

print(

  “Updated Dict is: “

  , dict)

dict1 = ‘key4’: ‘is’, ‘key5’: ‘fabulous’

dict.update(dict1)

print(dict)

dict.update(newkey1=’portal’)

print(dict)

Output:

Current Dict is: ‘key1’: ‘geeks’, ‘key2’: ‘for’

Updated Dict is: ‘key1’: ‘geeks’, ‘key2’: ‘for’,

‘key3’: ‘geeks’

‘key1’: ‘geeks’, ‘key2’: ‘for’, ‘key3’: ‘geeks’,

‘key4’: ‘is’, ‘key5’: ‘fabulous’

‘key1’: ‘geeks’, ‘key2’: ‘for’, ‘key3’: ‘geeks’,

‘key4’: ‘is’, ‘key5’: ‘fabulous’, ‘newkey1’: ‘portal’

Method 3: Add new keys using the

__setitem__ method

The __setitem__ method to add a key-value pair to a dict using the __setitem__ method. It should be avoided because of its poor performance (computationally inefficient). 

Python3

dict = ‘key1’: ‘geeks’, ‘key2’: ‘for’

dict.__setitem__(‘newkey2’, ‘GEEK’)

print(dict)

Output:

‘key2’: ‘for’, ‘newkey2’: ‘GEEK’, ‘key1’: ‘geeks’

 Method 4: Add new keys using the ** operator 

We can merge the old dictionary and new key/value pair in another dictionary. Using ** in front of key-value pairs like  **‘c’: 3 will unpack it as a new dictionary object.

Python3

dict =

‘a’: 1, ‘b’: 2

new_dict = **dict, **’c’: 3

print(dict)

print(new_dict)

Output:

‘b’: 2, ‘a’: 1

‘b’: 2, ‘c’: 3, ‘a’: 1

Method 5: Add new keys using the “in” operator and IF statements.

If the key is not already

present in the dictionary, the key will be added to the dictionary using the if statement. If it is evaluated to be false, the “Dictionary already has a key” message will be printed.

Python3

mydict = “a”: 1, “b”: 2, “c”: 3

if “d” not in mydict:

    mydict[“d”] = “4”

else:

    print(“Dictionary already has key : One. Hence value is not overwritten “)

print(mydict)

Output:

‘a’: 1, ‘b’: 2, ‘c’: 3, ‘d’: ‘4’

Method 6: Add new keys using a for loop and enumerate() method

Make a list of elements. Use the enumerate() method to iterate the list, and then add each item to the dictionary by using its index as a key for each value.

Python3

list1 =

“a”: 1, “b”: 2, “c”: 3

list2 = [“one: x”, “two:y”, “three:z”]

for i, val in enumerate(list2):

    list1[i] = val

print(list1)

Output:

‘a’: 1, ‘b’: 2, ‘c’: 3, 0: ‘one: x’, 1: ‘two:y’, 2: ‘three:z’

Example 7: Add Multiple Items to a Python Dictionary with Zip

In this example, we are using a

zip method of python for adding keys and values to an empty dictionary python. You can also use an in the existing dictionary to add elements in the dictionary in place of a dictionary =

Python3

dictionary =

keys = [‘key2’, ‘key1’, ‘key3’]

values =

[‘geeks’, ‘for’, ‘geeks’]

for key, value in zip(keys, values):

    dictionary[key] = value

print(dictionary)

Output:

‘key2’: ‘geeks’, ‘key1’: ‘for’, ‘key3’: ‘geeks’

How do you add a value to a key in Python?

Add Values to Dictionary in Python. Assigning a value to a new key.. Using dict. update() method to add multiple key-values.. For Python 3.9+, use the merge operator ( | ).. For Python 3.9+, use the update operator ( |= ).. Creating a custom function.. Using __setitem__() method (It is not recommended)..

How do you assign a key to a dictionary in Python?

You can add key to dictionary in python using mydict[“newkey”] = “newValue” method. Dictionaries are changeable, ordered, and don’t allow duplicate keys. However, different keys can have the same value.

How do you call a key in Python?

Let’s discuss various ways of accessing all the keys along with their values in Python Dictionary.. Method #1 : Using in operator.. Method #2 : Using list comprehension.. Method #3 : Using dict.items(). Method #4 : Using enumerate().

How do I add a key value pair to a dictionary?

Below are the two approaches which we can use.. Assigning a new key as subscript. We add a new element to the dictionary by using a new key as a subscript and assigning it a value. … . Using the update() method. … . By merging two dictionaries..

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