Create a Python dictionary that returns a list of values for each key. The key can be whatever type you want.
Design the dictionary so that it could be useful for something meaningful to you. Create at 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 key\value 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'}