An Overview of Dictionaries in Python


All these above questions will be answered here.

Dictionaries play an important role in Data World. 
Imagine ….
You are working in a school as a counselor, and want to keep track of the student in each class.
You can put the strength of students in a list, here I am taking a group of 5 class dataset.


And to keep a track of which class contains a certain no. of students, we will create another list with the class name.

classes =[’10A’,’12B’,’10B’,’11A’,’10C’]

Now suppose that you want to find out how many students are there in the “11A” class.
Firstly you have to figure out where in the list is “11A”; so that you can use this position to get the correct student number.

So, we will use index(), to get the index of “11A” in class, like this:

ind_11A = classes.index(’11A’)

Now we can use this index to subset the student list, to get the students corresponding to ’11A’.


Out: 3


Out: 41

Yeah, so here we built 2 lists and used the index to connect corresponding elements in both the lists.
And, it worked!
But, it’s a pretty terrible approach, in other words, it’s not convenient.

Wouldn’t it be easier if we had a way to connect each class to its student, without using any index??

This is where DICTIONARY comes into the picture.

Let us convert the class data to a dictionary….

It starts with “{” (curly braces), and inside curly braces, you have a bunch of what we call key: value pairs.
Keys and values are separated by : (colon).

In our case, the keys are class names, and values are the corresponding students.

school = {’10A’ : 52, ’12B’ : 35, ’10B’ : 65, ’11A’ : 41, ’10C’ : 53}

If now you want to find out the number of students in “11A”, you can simply type school and then the string “11A” inside the
square brackets.

Out: 41 

In simple words, you pass the key in square brackets and you get the corresponding value.

“THE KEY OPENS THE DOOR TO THE VALUE”: pretty poetic, isn’t it?

This approach is not only intuitive but also very efficient, because python can make the lookup of these keys very fast,
even for huge dictionaries.

A point should always be remembered while using dictionaries, that is:
The key should be unique.


  • To add a new key to the existing dictionary –       school[’12A’] = 45
  • To remove a key –          del(school[’12A’])
  • To check if the key is in dictionary –        “10A” in school
  • To copy a dictionary into another dictionary –       school2 = school.copy()
  • To create dictionaries having dictionaries –       Dict = { ‘Dict1’: {1: ‘G’, 2: ‘F’, 3: ‘G’}, ‘Dict2’: {‘Name’: ‘Geeks’, 1: [1, 2]} } 
  • To get a certain element from just one dictionary –      Dict[‘Dict1’][1]

So, these were some basic functions related to dictionaries. I hope now you are well versed in the benefits of using dictionaries.

Thank you for reading!