Data Structure is a collection of data types and set of rules with a format of organizing, managing and storage which can be used for efficient accessing and modification. Data structures are used in every field for storing and organizing data in the computer.


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Python - Data structures cheat sheet


This Python Data Structure cheat sheet will help you understand what Data Structure is and the basic concepts and commands you must know to get started with it.


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Data Structure: It is a way of organizing data that contains the items stored and their relationship to each other

DATA STRUCTURES with PythonThe areas in which Data Structures are applied:

  • Compiler design
  • Operating system
  • Database Management System
  • Statistical Analysis Package
  • Numerical Analysis
  • Graphics
  • Artificial Intelligence
  • Simulations

Data structures used in the following areas:

  • RDBMS: Array (Array of structure)
  • Network data model: Graph
  • Hierarchical Data model: Trees


Types of Data Structures:

Primitive Data Structures:

  • Integer: It is used to represent numeric data, more specifically whole numbers from negative infinity to infinity

Example: 4, 5, -1 etc

  • Float: It stands for floating point number

Example: 1.1,2.3,9.3 etc.

  • String: It is a collection of Alphabets, words or other characters. In python it can be created by using a pair of single or double quotes for the sequence


x = ‘Cake’

y = ‘’Cookie’’

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Certain operations can be performed on a string:

  • We can use * to repeat the string for a specific number of times

Example: x*2

  • String can be sliced, that is to select parts of the string

Example: Coke

z1 = x[2:]
# Slicing
z2 = y[0] + y[1]

Output: ke
  • To capitalize the strings


  • To retrieve the length of the strings


str1 = "Cake 4 U"
str2 = "404"
  • To replace parts of a string with another string


 str1.replace('4 U', str2)
  • Boolean: It is a built-in data type that can take the values TRUE or FALSE


Non- Primitive Data Structures:

  • Array: It is a compact way of collecting data types where all entries must be of the same data type.

Syntax of writing an array in python:

import array as arr
a = arr.array("I",[3,6,9])
  • Linked list: List in Python is used to store collection of heterogeneous items. It is described using the square brackets [] and hold elements separated by comma


x = [] # Empty list

The list can be classified into linear and non-linear data structures
Linear data structures contain Stacks and queues
Non-linear data structures contain Graphs and Trees

  • Stack: It is a container of objects that can be inserted or removed according to LIFO (Last in First Out) pop() method is used during disposal in Python


stack.pop() # Bottom -> 1 -> 2 -> 3 -> 4 -> 5 (Top)
stack.pop() # Bottom -> 1 -> 2 -> 3 -> 4 (Top)

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  • Queue: It is a container of objects that can be inserted or removed according to FIFO (First in First Out)
  • Graph: It is a data structure that consists of a finite set of vertices called nodes, and a finite set of ordered pair (u,v) called edges. It can be classified as direction and weight
  • Binary Tree: Tree is a hierarchical data structure. Here each node has at most two children
  • Binary Search Tree: It provides moderate access/ search and moderate insertion/ deletion
  • Heap: It is a complete tree and is suitable to be stored in an array, it is either MIN or Max
  • Hashing: Collection of items that are stored in a way that it becomes easy to find them is hashing


Types of Data Structures


Lists and tuples (In Python):

Ordered sequence of values indexed by integer numbers. Tuples are immutable

  • To initialize empty list /tuple:


Lists: myList = []
Tuples: myTuple = ()
  • To specify size of tuple/list:


  • To get an element in position x in list/tuple:


 "x" in myList­OrT­uple
  • Index of element ‘X’ of list/tuple


myLis­tOr­Tup­le.i­nd­ex(­"­x") -- If not found, throws a Value­Error exception
  • Number of occurrences of X in list/tuple:


  • Update an item of List/tuple:


Lists: myList[x] = "x"
Tuples: tuples are immutable!
  • Remove element in position X of list/tuple:


Lists: del myList[x]
Tuples: tuples are immutable!
  • Concatenate two lists/tuples:
Lists: myList1 + myList2
Tuples: myTuple1 + myTuple2
Concatenating a List and a Tuple will produce a TypeE­rror exception
  • Insert element in position x of a list/t­uple


Lists: myLis­t.i­nse­rt(x, "value")
Tuples: tuples are immutable!
  • Append “­x” to a list/t­uple:
Syntax: Lists: myList.append("x")
Tuples: tuples are immutable!
  • Convert a list/tuple to tuple/list:
Syntax: List to Tuple: tuple(myList)
Tuple to List: list(­myT­uple)



It is an unordered collection with no duplicate elements. It supports mathematical operations like union, inters­ection, difference and symmetric differ­ence.

  • To initialize an empty set:
Syntax: mySet = set()
  • Initialize a non-empty set
Syntax: mySet = set(el­ement1, elemen­t2...)
  • To add element X to the set
  • Remove element “­x” from a set:


Method 1:­mov­e("x­") -- If "­x" is not present, raises a KeyErorr
Method 2: mySet.di­sca­rd(­"­x") -- Removes the element, if present
  • Remove every element from the set
  • Check if “­x” is in the set
Syntax: "x" in mySet
  • Union of two sets


Method 1: mySet1.union(mySet2)
Method 2: mySet1 | mySet2
  • Inters­ection of two sets


Method 1: mySet1.intersect(mySet2)
Method 2: mySet1 & mySet2
  • Difference of two sets


Method 1: mySet1.difference(mySet2)
Method 2: mySet1 - mySet2
  • Symmetric difference of two sets


Method 1: mySet1.symmetric_difference(mySet2)
Method 2: mySet1 ^ mySet2
  • Size of the sets:



Want to learn queues in Python? Refer to our blog on Python Queue and make exciting projects!



It is an unordered set of key value pairs

  • Initialize an empty Dict


myDict = {}
  • Add an element with key “­k” to the Dict


myDic­t["k­"] = value
  • Update the element with key “­k”


myDic­t["k­"] = newValue
  • Get element with key “­k”


myDic­t["k­"] -- If the key is not present, a KeyError is raised
  • Check if the dictionary has key “­k”


"k" in myDict
  • Get the list of keys


  • Get the size of the dictionary


  • Delete element with key “­k” from the dictionary


del myDict­["k"]
  • Delete all the elements in the dictionary



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Algorithms and the complexities:

Algorithm Best case Average case Worst case Remarks
Selection sort ½ n 2 ½ n 2 ½ n 2 n exchanges,
quadratic is the best case
Insertion sort n ¼ n 2 ½ n 2 Used for small or partial-sorted arrays
Bubble sort n ½ n 2 ½ n 2 Rarely useful,
Insertion sort can be used instead
Shell sort n log3 n unknown c n 3/2 Tight code,
Sub quadratic
Merge sort ½ n lg n n lg n n lg n n log n guarantee;
Quick sort n lg n 2 n ln n ½ n 2 n log n probabilistic guarantee;
fastest in practice
Heap sort n 2 n lg n 2 n lg n n log n guarantee;
in place


Symbol Table:

Worst case Average case
Data Structure Search Insert Delete Search Insert Delete
Sequential search n n n n n n
Binary search log n n n log n n n
Binary search tree n n n log n log n sqrt(n)
Red-black BST log n log n log n log n log n log n
Hash table n n n 1 1 1

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