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Dictionaries

Dictionary is one of the built-in data types in Python. Python’s dictionary is example of mapping type. A mapping object ‘maps’ value of one object with another.

Only a number, string or tuple can be used as key.
Python doesn’t accept mutable objects such as list as key, and raises TypeError.
You can assign a value to more than one keys in a dictionary, but a key cannot appear more than once in a dictionary.

Ex:

capitals = {"Telangana":"Hyderabad", "Karnataka":"Bengaluru"}
numbers = {10:"Ten", 20:"Twenty"}
d1 = {"Fruit":["Mango","Banana"], "Flower":["Rose", "Lotus"]}
d2 = {('India, USA'):'Countries', ('New Delhi', 'New York'):'Capitals'}
d3 = {["Mango","Banana"]:"Fruit", "Flower":["Rose", "Lotus"]}  --> Error

The get() method in Python’s dict class returns the value mapped to the given key. dict.get("key") gives value of the key.

Updating dictionaries

There are few ways.

Update with Another Dictionary. Ex: d1.update(d2).
Update with Iterable. Ex: d1.update([(k1, v1), (k2, v2)])
Update with Keyword Arguments Ex: d1.update(k1=v1, k2=v2)
Using the Union Operator ( ). Ex: d3 = d1 | d2 Or d1 |= d2
Using the Unpack Operator Ex: d3 = {**d1, **d2}

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: \n", marks)
marks1 = {"Sharad": 51, "Mushtaq": 61, "Laxman": 89}
newmarks = {**marks, **marks1}
print ("marks dictionary after update: \n", newmarks)

Result:

marks dictionary before update:
{'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update:
{'Savita': 67, 'Imtiaz': 88, 'Laxman': 89, 'David': 49, 'Sharad': 51, 'Mushtaq': 61}

Remove dictionary items

Using del Keyword
The pop() method of dict class causes an element with the specified key to be removed from the dictionary.
The popitem() method in dict() class doesn’t take any argument. It pops out the last inserted key-value pair, and returns the same as a tuple. Ex: val = dict.popitem()
The clear() method in dict class removes all the elements from the dictionary object and returns an empty object.

Nested dictionaires

Ex:

marklist = {
   "Mahesh" : {"Phy" : 60, "maths" : 70},
   "Madhavi" : {"phy" : 75, "maths" : 68},
   "Mitchell" : {"phy" : 67, "maths" : 71}
}

mydict = {'Name':'Test','Surname':'Test1','Age':36,'Salary':6500.20}
print("My name is :",mydict['Name'])
print("My Salary :",mydict['Salary'])

mydict['wife'] = "Testy"
print(mydict)

mydict['Name'] = "Test Tost"
print(mydict)

print(mydict.keys())
print(mydict.values())
print(mydict.items())

price_lookup= {'apple':2.99,'banana':1.99,'orange':1.49}
print("Price of Orange : ",price_lookup['orange'])

d = {'k1':123,'k2':[0,'a',2],'k3':{'Orange':1.49,'apple':1.99}}
print(d['k1'])
print("Dict list : ",d['k2'])
print("Dict list value : ",d['k2'][2])
print("Dict list value : ",d['k2'][1].upper())

print("Dict dict : ",d['k3'])
print("Dict dict value :",d['k3']['apple'])

Result:

My name is : Test
My Salary : 6500.2
{'Name': 'Test', 'Surname': 'Test1', 'Age': 36, 'Salary': 6500.2, 'wife': 'Testy'}
{'Name': 'Test Tost', 'Surname': 'Test1', 'Age': 36, 'Salary': 6500.2, 'wife': 'Testy'}
dict_keys(['Name', 'Surname', 'Age', 'Salary', 'wife'])
dict_values(['Test Tost', 'Test1', 36, 6500.2, 'Testy'])
dict_items([('Name', 'Test Tost'), ('Surname', 'Test1'), ('Age', 36), ('Salary', 6500.2), ('wife', 'Testy')])
Price of Orange :  1.49
123
Dict list :  [0, 'a', 2]
Dict list value :  2
Dict list value :  A
Dict dict :  {'Orange': 1.49, 'apple': 1.99}
Dict dict value : 1.99

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