Dictionary (Back to basics)
Definition:
1) Dictionaries are used to store data in key-value pair form.
'name' : 'Lamborghini'
so the 'name' is the key and 'Lamborghini' is the value.
2) A dictionary is a collection of ordered(in Python 3.7 or later) and unordered(in Python 3.6 or earlier). It does not allow duplicates.
for example:
{'name':'Bugatti','name':'Buggati' } not possible due to duplicate key value pair
or
{'name':'Alfa Romeo','name':'Maserati'} not possible due to duplicate key and if used then the second key-value pair is displayed instead of the first item.
3) Dictionaries are written within curly brakets and have key-value pairs
car = {'brand':'Ford','model':'Mustang','year':1964}
print(car)
4) Dictionary length - it determines how many items a dictionary has using the len() function. It is important to note that an item is key-value pair.
so in the previous example 'model':'Mustang' is a item cause it is a key-value pair
now if we apply the function to the previous example like:
p = len(car)
print(p)
5) The key of the dictionary can never be of any mutable datatype example list. **very important
example:
p = { ['Brands','Models']:"Koenigsegg ONE"}
print(p)
If you try to run the program you will get an error TypeError: unhashable type: 'list'
6)The key of the dictionary can only be of immutable datatypes example numbers,tuple and string.
example:
1)
p = {('Brands','Models'):"Koenigsegg One"}
print(p)
2)
p = {1:'Ford',2:'Mahindra',3:'TATA'}
print(p)
3)
p ={'Ford':'Mustang','Chevrolet':'Camaro'}
print(p)
7) To display a dictionary in proper format we need to use the module:
import json (json stands for javascript object notation)
then we need to use the function present inside the module that function is dumps()
so we need to use like this:
import json
p = {'brand':'Mahindra','model':'XUV 700','year':2023}
print(json.dumps(p,indent=2)
it will be displayed in this format:
{
"brand": "Mahindra",
"model": "XUV 700",
"year": 2023
}
8) Accessing items: To access the items of a dictionary by refering to its key name,inside square brackets.
p={
"brand": "Mahindra",
"model": "XUV 700",
"year": 2023
}
z = p["year"]
print(z)
we will get 2023 as the answer
we can do this in another way
z = p.get("year")
print(z)
9) To display only the keys of the dictionary we will use the function:
z = p.keys()
Output:
dict_keys(['brand', 'model', 'year'])
10) To add new item to a dictionary
p["Price"]="20 lacs"
so the dictionary will look like this
p={
"brand": "Mahindra",
"model": "XUV 700",
"year": 2023,
"Price":"16 lacs"
}
print(p)
11) The values() function will return a list of all the values in the dictionary
z = p.values()
print(z)
Output:
dict_values(['Mahindra', 'XUV 700', 2023, '16 lacs'])
12) The items() function will return each item in a dictionary, as tuple in a list
z = p.items()
print(z)
Output:
dict_items([('brand', 'Mahindra'), ('model', 'XUV 700'), ('year', 2023), ('price', '16 lacs')])
13) Changing a value of a dictionary using key
p={
"brand": "Mahindra",
"model": "XUV 700",
"year": 2023,
"Price":"16 lacs"
}
so let's change the year to 2024
p['year']=2024
The dictionary will look something like this
p={
"brand": "Mahindra",
"model": "XUV 700",
"year": 2024,
"Price":"16 lacs"
}
14) Checking the presence of a key using "in" keyword
p={
"brand": "Mahindra",
"model": "XUV 700",
"year": 2024,
"Price":"16 lacs"
}
if "year" in p:
print("Oshnik will buy",p["brand"],p["model"])
Output:
Oshnik will buy Mahindra XUV 700
15) Updating a dictionaryusing update() method
we need to pass key:value pairs to update a dictionary
p = {
'name':'Oshnik Kundu',
'initials':'OK',
'age':16
}
p.update({'age':17})
print(p)
Output: {'name':'Oshnik Kundu','initials':'OK','age'17}
16) Removing items from dictionary
There are different ways like pop(),popitem(),del,clear().
(i) The pop() method removes the item with the specified key name
p={"brand": "Mahindra","model": "XUV 700","year": 2023,"Price":"16 lacs"}
p.pop("Price")
print(p)
Output:
{"brand": "Mahindra","model": "XUV 700","year": 2023}
(ii) The popitem() method removes the last item.
p={"brand": "Mahindra","model": "XUV 700","year": 2023}
p.popitem()
print(p)
Output:
{"brand": "Mahindra","model": "XUV 700"}
(iii) The del keyword removes the item with the specified key name:
p={"brand": "Mahindra","model": "XUV 700","year": 2023}
del p["model"]
print(p)
Output:
{"brand": "Mahindra","year": 2023}
(iv) The clear() method empties the dictionary
p={"brand": "Mahindra","model": "XUV 700","year": 2023}
p.clear()
print(p)
Output:
{}
17) Looping through a dictionary:
You can loop through a dictionary using a for loop
(i) To print all the keys of the dictionary one by one
p={"brand": "Mahindra","model": "XUV 700","year": 2023}
for k in p:
print(k)
Output:
brand
model
year
(ii) To print all the values of the dictionary one by one
p={"brand": "Mahindra","model": "XUV 700","year": 2023}
for k in p:
print(p[k])
Output:
Mahindra
XUV 700
2023
(iii) To print key and values together one by one items
for k,v in p.items():
print(k,v)
Output:
brand Mahindra
model XUV 700
year 2023
