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Dictionary In Python: Everything You Need To Know About Python Dictionary

Published on May 22,2019 630 Views

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Python programming language is one of the most popular programming languages. It has numerous applications and implementations which make it unique and desirable to developers. Dictionary in python is one such concept, which is unique and gives an edge to python over other programming languages. It is a collection like a list or set but has unique features which will be discussed in this blog. So let us start by taking a look at pointers that will be discussed here:

What Is A Dictionary In Python?

It is a collection data type just like a list or a set, but there are certain features that make python dictionary unique. A dictionary in python is not ordered and is changeable as well. We can make changes in a dictionary unlike sets or strings which are immutable in nature. Dictionary contains key-value pairs like a map that we have in other programming languages. A dictionary has  indexes. Since the value of the keys we declare in a dictionary are always unique, we can use them as indexes to access the elements in a dictionary.

Also, a dictionary does not have any duplicate members. Although the value elements in the key value pairs can contain duplicate values.

Why Use A Dictionary In Python?

First of all, it is not like any other object or data type in python programming language. A dictionary has key value pairs resembling a map. It is often used for unordered data with distinct key values. 

It is similar to a real life dictionary. We have distinct keys which we can use to fetch the values specified in them. In case of dictionary, even though there are no duplicate members, we can mention duplicate members in the value elements. Now that we know, why we use a dictionary, lets try to understand how it is different from lists in python.

Lists vs Dictionary

ListsDictionary
 Ordered Not ordered
 Access elements use index values Access elements use keys as index values
 Collection of elements Collection of key value pairs
 Allows duplicate members No duplicate members
 Preferred for ordered data Preferred for data with unique key values

How To Implement A Dictionary?

To declare a dictionary in python, we use the curly brackets. The keys and values are separated with a colon and the pairs are separated with a comma.


mydictionary = { 'key1' : 'value1' , 'key2': 'value2' , 'key3': 'value3'}
print(mydictionary)

Operations In A Python Dictionary

Accessing an element


mydictionary = { 1: 'edureka' , 2: 'python' , 3: 'data science'}
mydictionary[1]
#this will get the key value pair with the key 1.
mydictionary.get(1)
#this is another function which will serve the same purpose.

Replacing an element


mydictionary = { 1: 'edureka', 2: 'python' , 3: 'data science'}
mydictionary[3] = 'artificial intelligence'
print(mydictionary)
#this will replace the value at key 3 to artificial intelligence.

Removing an element


mydictionary = { 1:'edureka' , 2 : 'python', 3: 'data science'}
del mydictionary[3]
print(mydictionary)
#this will remove the key value pair from the dictionary with the specified key.

Other Operations

 Following are the operations we have for dictionary in python:

  • clear()
  • copy()
  • values()
  • update()
  • fromkeys()
  • get()
  • items()
  • keys()
  • pop()
  • popitem()
  • setdefault()

clear( ) – removes all the elements from the dictionary.


a = { 1: 2 , 2: 3 , 3: 5}
a.clear()
print(a)
#you will get a empty dictionary as the output.

copy( ) – returns a copy of the dictionary.


a = {1:2, 2: 3, 3: 4}
b = a.copy()
print(b)
#b will be a copy of the dictionary a.

values( ) – returns all the values in a dictionary.


a = {1: 2, 2: 3, 3:4}
a.values( )
#this will get you the list of all the values in the dictionary.

update( ) – it updates the values of the dictionary with the specified key value pairs.


a = {1 : 2, 2: 3, 3: 5}
a.update({4: 6})
#this will update the dictionary with the specified key value pair.

fromkeys( ) – returns a dictionary with the specified keys and values.


a = {1: 'edureka' , 2: 'data science'}
b = {1: 2, 2: 3, 3: 'python'}
a.Fromkeys(b)
#this will get the dictionary with the specified keys and values.

items( ) – returns the list for a tuple of each key value pair in the dictionary.


a = {1: 'edureka', 2; 'python'}
a.items()
#this will get the list of tuple for each key value pair.

keys( ) – returns a list containing all the keys in the dictionary.


a = { 1: 'edureka' , 2 : 'python' , 3 : 'data science'}
a.keys()
#this will get the list of all the keys from the dictionary.

pop( ) – removes the element with the specified key.


a = { 1: 'edureka' , 2: 'data science' , 3: 'python' }
a.pop(3)
#this will remove the value 'python' from the dictionary.

popitem( ) – removes the last inserted key values pair from the dictionary.


a = { 1: 'edureka' , 2: 'python' , 3: 'data science'}
a.popitem()
#this will remove the last inserted key value pair from the dictionary.

setdefault( ) – returns the value of the specified key, if not present insert the key with the specified value.


a = { 1: 'edureka' , 2: 'python' }
a.setdefault(1, 'edureka')

Dict( ) constructor

Dictionary constructor is used to declare a dictionary in python.


a = dict( 1= 'edureka' , 2= 'python' , 3= 'data science')
print(a)
#this will declare a dictionary with the name a and specified key value pairs.

Use Case – Nested Dictionary

Nested dictionary is nothing but a dictionary which incorporates another dictionary. Let us implement a dictionary where we have the statistical data for all the Indian batsmen. We will implement a dictionary with the batsmen names and incorporate other dictionary with the statistics inside the same dictionary to make it a nested dictionary. We will also use the pandas library to get the stats into a dataframe for better understanding.

import pandas as pd
squad = {'Batsmen': {'Rohit Sharma': {'Matches': 206,
                                      'Runs': 8010,
                                      'Average':47.4,
                                      'Highest Score': 264 },
                     'Shikhar Dhawan': {'Matches':128,
                                        'Runs': 5355,
                                        'Average': 44.62,
                                        'Highest Score': 143},
                     'Virat Kohli': {'Matches': 227,
                                     'Runs': 10843,
                                     'Average': 59.58,
                                     'Highest Score': 183}}
df = pd.DataFrame(squad['Batsmen'])
print(df)

This will print the data frame of the stats of the batsmen from the dictionary. Similarly, you can make this dictionary for bowlers, all rounders and wicket keepers to practice the implementation of nested dictionary.

output-dictionary in python-edureka

In this blog, we have understood the concept of dictionary in python. We have learnt to implement a dictionary and various operations that we can perform on a dictionary. We also covered dictionary constructor and nested dictionary. If you want to kick start your learning in python, you may enroll to Edureka’s python certification program to guide your career to success as a python developer.

Have any questions? mention them in the comments, we will get back to you.

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