Python Data Structures (With Examples)

Deepanshu Bhalla 2 Comments

This post explains the data structures used in Python, along with examples.

Python Data Structures

In python, there are many data structures available. They are as follows :

  1. String
  2. List
  3. Tuple
  4. Dictionary
  5. Sets


String is a sequence of characters.

How to create a string in Python?

You can create string using a single or double quote.

mystring = "Hello Python3.6"

# Output
# Hello Python3.6

Note : You can also use multiple single or double quotes to define string.

How to include quotes within a string?

mystring = r'Hello"Python"'

# Output
# Hello"Python"

How to extract Nth letter or word?

You can use the syntax below to get first letter.

mystring = 'Hi How are you?'

# Output
# 'H'

mystring[0] refers to first letter as indexing in python starts from 0. Similarly, mystring[1] refers to second letter. To pull last letter, you can use -1 as index.

To get first word

mystring.split(' ')[0]

# Output
# Hi

How it works -

1. mystring.split(' ') tells Python to use space as a delimiter.

Output : ['Hi', 'How', 'are', 'you?']

2. mystring.split(' ')[0] tells Python to pick first word of a string.


Unlike string, list can contain different types of objects such as integer, float, string etc.

  1. x = [142, 124, 234, 345, 465]
  2. y = [‘A’, ‘C’, ‘E’, ‘M’]
  3. z = [‘AA’, 44, 5.1, ‘KK’]
Get List Item

We can extract list item using Indexes. Index starts from 0 and end with (number of elements-1).

Syntax : list[start : stop : step]

  1. start : refers to starting position.
  2. stop : refers to end position.
  3. step : refers to increment value.

k = [124, 225, 305, 246, 259]
k[0] # returns 124
k[1] # returns 225
k[-1] # returns 259

Explanation :

k[0] picks first element from list. Negative sign tells Python to search list item from right to left. k[-1] selects the last element from list.

To select multiple elements from a list, you can use the following method :

k[:3] # returns [124, 225, 305]
k[0:3] # also returns [124, 225, 305]
k[::-1] # reverses the whole list and returns [259, 246, 305, 225, 124]
Sort list

sorted(list) function arranges list in ascending order.

sorted(list, reverse=True) function sorts list in descending order.

sorted(k) # returns [124, 225, 246, 259, 305]
sorted(k, reverse=True) # returns [305, 259, 246, 225, 124]
Add 5 to each element of a list

In the program below, len() function is used to count the number of elements in a list. In this case, it returns 5. With the help of range() function, range(5) returns 0,1,2,3,4.

x = [1, 2, 3, 4, 5]
for i in range(len(x)):
    x[i] = x[i] + 5

# Output   
# [6, 7, 8, 9, 10]

It can also be written like this -

for i in range(len(x)):
   x[i] += 5

Combine / Join two lists

The '+' operator is concatenating two lists.

X = [1, 2, 3]
Y = [4, 5, 6]
Z = X + Y

# Output
# [1, 2, 3, 4, 5, 6]

Sum of values of two list

X = [1, 2, 3]
Y = [4, 5, 6]

import numpy as np
Z = np.add(X, Y)

# Output
# [5 7 9]

Similarly, you can use np.multiply(X, Y) to multiply values of two list.

Repeat List N times

The '*' operator is repeating list N times.

X = [1, 2, 3]
Z = X * 3

# Output  
# [1, 2, 3, 1, 2, 3, 1, 2, 3]

Note : The above two methods also work for string list.

Modify / Replace a list item

Suppose you need to replace third value to a different value.

X = [1, 2, 3]

# Output
# [1, 2, 5]

Add / Remove a list item

We can add a list item by using append method.

X = ['AA', 'BB', 'CC']

# Result
# ['AA', 'BB', 'CC', 'DD']

Similarly, we can remove a list item by using remove method.

X = ['AA', 'BB', 'CC']

# Result : ['AA', 'CC']


Like list, tuple can also contain mixed data. But tuple cannot be mutable or changed once created whereas list can be mutable or modified.

Another difference is a tuple is created inside parentheses ( ). Whereas, list is created inside square brackets [ ]


mytuple = (123,223,323)
City = ('Delhi','Mumbai','Bangalore')
Perform for loop on Tuple

for i in City:

# Output
# Delhi
# Mumbai
# Bangalore
Tuple cannot be altered

Run the following command and check error.

X = (1, 2, 3)

TypeError: 'tuple' object does not support item assignment.


It works like an address book wherein you can find an address of a person by searching the name. In this example. name of a person is considered as key and address as value. It is important to note that the key must be unique while values may not be. Keys should not be duplicate because if it is a duplicate, you cannot find exact values associated with key. Keys can be of any data type such as strings, numbers, or tuples.

Create a dictionary

It is defined in curly braces {}. Each key is followed by a colon (:) and then values.

teams = {'Dave' : ['teamA','teamAA', 'teamAB'],
         'Tim'  : ['teamB','teamBB','teamBC'],
         'Babita' : ['teamC','teamCB','teamCC']

Extract Keys and Values of Dictionary
  • teams.keys() returns keys i.e. ['Dave', 'Tim', 'Babita']
  • teams.values() returns values i.e. [['teamA', 'teamAA', 'teamAB'], ['teamB', 'teamBB', 'teamBC'], ['teamC', 'teamCB', 'teamCC']]
  • teams.items() returns both keys and values.
Find Values of a particular key


# Output
# ['teamA', 'teamAA', 'teamAB']
Delete an item
In the code below, we are removing 'Babita' from teams dict.

del teams['Babita']

# Output
# {'Dave': ['teamA', 'teamAA', 'teamAB'], 
# 'Tim': ['teamB', 'teamBB', 'teamBC']}
Add an item
Here we are adding one more key named 'Deep' and value against it is 'team D'.

teams['Deep'] = 'team D'

# Output
# {'Dave': ['teamA', 'teamAA', 'teamAB'],
# 'Deep': 'team D',
# 'Tim': ['teamB', 'teamBB', 'teamBC']}

You can also create dictionary like the way it is shown below

d['a'] = 1
d['b'] = 2

# Output
# {'a': 1, 'b': 2}
How to create a dictionary from lists

Suppose you have keys and values stored in two separate lists. You can use and zip them to create a dictionary.

keys = ['a', 'b', 'c']
values = [1, 2, 3]
d1 = dict(zip(keys, values))


Sets are unordered collections of simple objects. They are mainly used to check whether an object is present in the set and compute mathematical operations such as intersection, union, difference etc.

X = set(['A', 'B', 'C'])
Q. Does 'A' exist in set X?
'A' in X
Result : True
Q. Does 'D' exist in set X?
'D' in X
Result : False
Q. How to add 'D' in set X?
Q. How to remove 'C' from set X?
Q. How to create a copy of set X?
Y = X.copy()
Q. Which items are common in both sets X and Y?
Y & X
Practical Examples : Python Data Structures

The examples below would help you to understand what kind of operations on data structures are commonly used in real-world.

1. How to find intersection and union of two lists

x = [1, 2, 3, 4]
y = [2, 3, 6, 5]

list(set(x) & set(y))
list(set(x) | set(y))

& symbol refers to 'and' condition which means common between two lists. | symbol refers to 'or' condition.

2. Check whether an item exist in list

x = [1, 2, 3, 4]
3 in x

# Output
# True
3. Check whether multiple items exist in list

all returns True only when all the items exist. Whereas any returns when any of the item exist.

all(i in x for i in [1,6])

# Output
# False

any(i in x for i in [1,6])

# Output
# True
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About Author:
Deepanshu Bhalla

Deepanshu founded ListenData with a simple objective - Make analytics easy to understand and follow. He has over 10 years of experience in data science. During his tenure, he worked with global clients in various domains like Banking, Insurance, Private Equity, Telecom and HR.

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