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## Introduction:

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.

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.

Further, if you want to learn Python Data Structure in depth, you can refer to the tutorial blog on Python

You can also download the printable PDF of this Data Structure cheat sheet

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

The 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

For Python

## Types of Data Structures:

### Primitive Data Structures:

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

E.g.: 4, 5, -1 etc

• Float: It stands for floating point number

E.g.: 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

E.g.: x = ‘Cake’

Certain operations can be performed on a string:

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

E.g.: x*2

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

E.g.: Coke

z1 = x[2:]

print(z1)

# Slicing

z2 = y[0] + y[1]

print(z2)

Output: ke

Co

• To capitalize the strings

• To retrieve the length of the strings

E.g.:

str1 = “Cake 4 U”

str2 = “404”

len(str1)

• To replace parts of a string with another string

E.g.: 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])

type(a)

• 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

E.g.: x = [] # Empty list

type(x)

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

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

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

print(stack)

• 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

## Lists and tuples (In Python):

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

• To initialize empty list /tuple:

Syntax: Lists: myList = []
Tuples: myTuple = ()

• To specify size of tuple/list:

Syntax: len(m­yLi­stO­rTu­ple)

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

Syntax: “x” in myList­OrT­uple

• Index of element ‘X’ of list/tuple

• Number of occurrences of X in list/tuple:

Syntax: myLis­tOr­Tup­le.c­ou­nt(­”­x”)

• Update an item of List/tuple:

Syntax: Lists: myList[x] = “x”

Tuples: tuples are immutable!

• Remove element in position X of list/tuple:

Syntax: 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

Syntax: 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)

## Sets:

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:

Syntax:

Method 1: mySet.re­mov­e(“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

Syntax: mySet.cl­ear()

• Check if “­x” is in the set

Syntax: “x” in mySet

• Union of two sets

Syntax:

Method 1: mySet1.union(mySet2)
Method 2: mySet1 | mySet2

• Inters­ection of two sets

Syntax:

Method 1: mySet1.intersect(mySet2)
Method 2: mySet1 & mySet2

• Difference of two sets

Syntax:

Method 1: mySet1.difference(mySet2)
Method 2: mySet1 – mySet2

• Symmetric difference of two sets

Syntax:

Method 1: mySet1.symmetric_difference(mySet2)
Method 2: mySet1 ^ mySet2

• Size of the sets:

Syntax: len(m­ySet)

## Dictionaries:

It is an unordered set of key value pairs

• Initialize an empty Dict

Syntax: myDict = {}

• Add an element with key “­k” to the Dict

Syntax: myDic­t[“k­”] = value

• Update the element with key “­k”

Syntax: myDic­t[“k­”] = newValue

• Get element with key “­k”

Syntax: myDic­t[“k­”] — If the key is not present, a KeyError is raised

• Check if the dictionary has key “­k”

Syntax: “k” in myDict

• Get the list of keys

Syntax: myDic­t.k­eys()

• Get the size of the dictionary

Syntax: len(m­yDict)

• Delete element with key “­k” from the dictionary

Syntax: del myDict­[“k”]

• Delete all the elements in the dictionary

Syntax: myDic­t.c­lear()

## 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; stable 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 †

With this, we come to an end of Python Data Structures Basic Cheat sheet. To get in-depth knowledge, check out our Python Training here, that comes with 24*7 support to guide you throughout your learning period. Intellipaat’s Python course will let you master the concepts of widely-used and powerful programming language Python. You will gain hands-on experience in working with the various Python packages like SciPy, NumPy, MatPlotLib, Lambda function and more. You will work on hands-on projects in the domain of python and apply it for various domains of big data, data science and machine learning.

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