Working with List and Dictionary

Krishan Meena

JAWAHAR NAVODAYA VIDYALAYA PUDUCHERRY

LIST

• They are container used to store any type of values.
• They are mutable (it mean you can change the element of list).
• A list can be created using square brackets.
• Each element separated by comma.

[ ]

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List samples

• A=[2,4,6,8] list with int members
• A=[] list with no members
• A=[‘k’,’l’,’m’,’n’] list with string members
• A=[1.2,2.2,3.2,4.20] list with float members
• A=[‘a’,2,3.0,’kris’] list with mixed values memebers

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Types of list

• 1. Empty list
• A=[]
• Or
• A=list()

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Types of list

• 2. long list
• Contain many element
• A=[1,2,5,6,8,9,10,22,56,89,98,96,56,2111,323,56,4879,2,3,6,79,56,8956,12]

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Types of list

• 3. nested list
• If a list element have itself list called nested list.
• A=[3,4,[5,6,7],8,9]
• Here the list length is only 5 but it containing 7 element because the[5,6] is treated as one element only.

Creating list from existing sequence

• We can use the following syntax to create the list from existing sequence:
• Variable name=list(sequence)
• A=list(‘hello’)
• It work only with string values not with integer.

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Creating list from existing sequence

Creating list from existing sequence

Creating list by user input

• A list can be input by user as string input. A String is a sequence and a string input to list( ) will treat the string sequence as a list:🡪

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Creating list by user input

Accessing list element

• It can be access same like string elements.

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Indexing

Accessing list elements

Forward

Indexing

Backward

Indexing

List

Length of the list

• We can find the length of a list using len() function.
• Example
• A=[1,2,3,4,5,6,7,8,9]
• len(A)
• Result 9

Quiz: 1

• If A=[1,2,3,[1,2,3],4,5,6,7,8]
• What will be the length of list ?

Indexing and slicing list

• Same like string slice
• A=[‘a’,’b’,’c’]
• A[2]
• Will result c as per indexing rule
• Slice
• A=[‘a’,’b’,’c’,1,2,3]
• A[2:6]

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Indexing and slicing list

• >>> a=['a','b','c',1,2,3]
• >>> a[2:5]
• ['c', 1, 2] result will display as per slicing rule
• >>>

Indexing and slicing list

We have to ignore

End limit value

Quiz : 2

• Generate auto list of the word “PYTHON” and print the list using for loop. Print in following pattern:🡪
• P
• Y
• T
• H
• O
• N

Membership operators

• Both in and not in operator
• a=list("PYTHON")
• print(a)
• if 'Y' in a:
• print("yes")
• else:
• print("no")

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Concatenation and replication operators

• The + and * operators
• The + operator used to join two list or more list.

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Quiz: 3

• #Question
• List1=list("python")
• List2=list("ix")
• List3=List1+List2
• print(List3)
• #Ans:

Quiz: 4

• #Question 2
• List1=["python"]
• List2=list("ix")
• List3=List1+List2
• print(List3)
• #Ans:

Quiz: 5

• #Question 3
• List1=["python","jnv"]
• List2=list("ix class")
• List3=List1+List2
• print(List3)
• #Ans:

* operator

• It will replicate the list
• List=[1,2,3]
• List*3
• [1,2,3,1,2,3,1,2,3]

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Slicing list

• Extracting the part of the list
• lst=[10,20,30,40,50,60,70,80,90]
• slice=lst[2:5]
• print(slice)
• [30,40,50] will result

List updating

• >>> list=['kn',12,23.56]
• >>> list[2]='lm'
• >>> list
• ['kn', 12, 'lm']
• >>> list[2]=56.56
• >>> list
• ['kn', 12, 56.56]

Working with list (Appending, updating, deleting on list)

• 1. Appending element to a list:
• Using append command for example :
• List=[12,24,36,48]
• List.append(60)
• Will add single item in the end of the list

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• 1. Appending element to a list:

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• >>> only one item can be added in list at end, not more than one

• 1. Appending element to a list:

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Value

added

At last

• 2. Updating list
• A list items can be update using index number and new value.

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Index number

New value

Updated value

Quiz: 6

• Quiz
• List=[11,22,33,44,55,67]
• Change the 67 into 66

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• 3. Deleting element form a list
• Using del command can remove single or all element identified by slice form a list
• Syntax:🡪
• del list[index number]

• 3. Deleting element form a list
• >>> list=[11,22,'jklk']
• >>> del list[2]
• >>> list
• [11, 22]

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List functions and methods

• They are built in functions and methods for list manipulation.
• Every list object you have created in python is actually an instance of list class.
• The list manipulation function can be use as per following syntax:
• <list object>.<method name>()

.index() function

• This function will return the index of the first matched item or member from the list.
• List.index(<item>)

.index() function

• Example : 1

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• List=[10,11,12,13,14,15]
• List.index(14)
• It will result as 4

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.index() function

• Example : 1

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• Lsit1=[12,13,14,15,14,16]
• Lsit1.index(14)
• it will find the first match and result as 2

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.index() function

• If the member or item does not exist in the list it will return error not in list
• Lsit1=[12,13,14,15,14,16]
• List1.index(56)
• As 56 is not a part the list1 so it will return error:
• 56 is not in list

.index() function

List.extend() function

• The extend() function is same like .append() function but the .append() function will add only one item at the end of the list but the extend() will add multiple element to a list or join lists.
• List.extend(<list>)

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List.extend() function

• >>> list1=[1,2,3,4,5]
• >>> list2=[5,6,5,6]
• >>> list1.extend(list2)
• >>> list1
• [1, 2, 3, 4, 5, 5, 6, 5, 6]
• >>> list2
• [5, 6, 5, 6]

Original list1 data

list1 Data after extend

Original list2 data

.insert() method

• It’s same like .append() and .extend() method used to insert element in the list.
• But the difference it can insert anywhere in list not at the end of the list.
• Structure :🡪
• list.insert(<position>,<item>)

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.insert() method

• >>> list1=['a','e','u']
• >>> list1.insert(2,'i')
• >>> list1
• ['a', 'e', 'i', 'u']
• >>>

.insert() method

.pop() function

• Will used to remove item or element from list and return the removed element as result.

Deleted item

Home work

• Difference between append and insert function in list explain with example
• Difference between pop and del function in list explain with example

Quiz: 7

• 1. list1=[12,16,18,19,20,18]
• list1.index(18) result ?
• 2. colour=[‘green’,’blue’,’red’,]
• colour.append(‘yellow’) result ?
• 3. t1=[‘a’,’b’,’c’]
• t1.extend(colour) result?
• 4. colour.insert(1,’pink’) result?
• 5. t1.pop(3) result ?

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.remove()

• .pop() will remove an element whose position is given what if you know the value of the element but if you don’t know the index position of the value in the list ?
• You can use remove() function
• list.remove(<value>)

.remove()

• >>> list1.remove('i')
• >>> list1
• ['e', 'o', 'u']
• >>>

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Removed

What if item does not exist?

What if item exist twice?

First occurrence will be removed not all.

.clear() function

• This method removes all the items from the list and makes list empty.
• For example:
• >>> list=[12,13,14,15,16,17,18]
• >>> list.clear()
• >>> list
• []

If you enter a value in clear brackets.

• List=[1,22,333,4444]
• >>> List.clear(22)
• Traceback (most recent call last):
• File "<pyshell#1>", line 1, in <module>
• List.clear(22)
• TypeError: clear() takes no arguments (1 given)

.count() function

• It will return the count of the element.
• >>> list=[10,11,12,13,15,14]
• >>> list.count(10)
• 1
• >>> list.insert(2,10)
• >>> list.count(10)
• 2

.count() function

• >>> name=["km","KM","mm"]
• >>> name.count(km)
• Traceback (most recent call last):
• File "<pyshell#1>", line 1, in <module>
• name.count(km)
• NameError: name 'km' is not defined
• >>> name.count("km")
• 1
• >>> name.count("KM")
• 1
• >>> name=["km","KM","km","mm"]
• >>> name.count("km")
• 2

Upper case and lower case treated differently

.count() function

• If the element does not exist in list it will result 0.

.reverse() function

• It will reverse the items or element of the list. It will not take any argument and does not return anything.

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.reverse() function

• >>> list
• [14, 15, 13, 12, 10, 11, 10]
• >>> list.reverse()
• >>> list
• [10, 11, 10, 12, 13, 15, 14]

.reverse() function

.sort() function

• This function use to sort the items in the list and by default it will sort in increasing order.
• List.sort()

.sort() function

Sorting in decreasing order

• It possible using two function reverse() and sort
• >>> list=[12,10,15,16,11,13]
• >>> list.sort(reverse=True)
• >>> list
• [16, 15, 13, 12, 11, 10]

Sorting in decreasing order

Comparing Lists:

• Two lists can be compared using standard comparison operators <. <=, >, >=, = =, !=. While comparing, Python internally compares individual elements of lists in lexicographical order. This means that, each corresponding element must compare equal and the two sequences must be of the same type i.e. having comparable types of values.

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Comparing Lists:

Two different lists

Comparing Lists:

Same values in both lists

Dictionaries

• Another way to organize collection of data items like string, list, tuple etc.
• Dictionaries are mutable
• the printed order element are always different from the order which you stored
• Basic structure of dictionary

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Creating dictionary

• color={“red”:”apple”,”green”:”grapes”}

Dictionary variable name

Dictionary keys

are unique

Dictionary values

Creating dictionary

• dict1 = { } # Empty Dictionary
• dict2 = {′English′ : 95, ′Maths′ : 98, ′Physics′ : 84, ′Chemistry′ : 88, ′IP′ : 99}
• dict3 = {'Alice':'Aravali','Nagesh':'Nilgiri','Shyam':'Shivalik','Uday':'Udaygiri'}

Creating dictionary

• dict4 = {1.1:1,2.2:2,3.3:3}
• dict5 = {1:1.1,2:2.2,3:3.3}
• dict6 = {'Even':[2,4,6,8,10],'Odd':[1,3,5,7,9],'Prime':[2,3,5,7]}
• dict7 = {(1,2):["Apple","Bat"],(3,4):["Cat","Dog"]}

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Creating dictionary

• Creating an empty dictionary: An empty dictionary can be created by assigning empty curly braces to a dictionary or by using the dictionary constructor, dict( )

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• Ex: student = { }
• student = dict( )

Creating dictionary

• Creating a Dictionary from name and value Pairs: Using the dict( ) constructor of dictionary, it is possible to create a new dictionary initialized from specified set of keys and values.
• Let see two different methods🡪

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Creating dictionary

Examples (Invalid Dictionaries):�

•  dict9 = {[1,2]:111,[3,4]:222}

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• dict10={{1:10}:100,2:20}

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# Key is mutable type – list

# Key is mutable type

– Dictionary in First Item

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Accessing element of dictionary

• With the help of key value
• Dictionary name[key]
• Example
• color={"green":"grapes","red":"apple"}
• >>> color["green"]
• 'grapes'

Membership Operators

• Both ‘in’ and ‘not in’ operators work on dictionaries. The ‘in’ returns True if a key is present in the dictionary and the ‘not in’ returns True if a key is not present in the dictionary
• Let see in example🡪

Membership Operators

Membership Operators

Membership Operators

Traversing a dictionary

• The for loop make easy to traversing the dictionary
• for item in dictionary:
• process each item here

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• Example: computer is dictionary with following item
• >>> computer={1:"computer",2:"mouse",3:"printer"}
• >>> for key in computer:
• print(key)

Traversing a dictionary

Traversing a dictionary

Quiz: 8

• Write a program to create a phone dictionary for all your friends and then print it.

Characteristic of dictionary

• They are mutable like list
• Unordered set
• Indexed by key not by numbers
• Key must be unique

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Updating key:value

Updating key:value

Deleting element from dic

• del dic [key]

Dictionary Functions and Methods:

• 1. len( ) :
• Returns the length or number of �key: value pairs of the dictionary passed as the argument

1. len( ) :�

Dictionary Functions and Methods:

• 2. get( )
• Returns the value corresponding to the key passed as the argument
• If the key is not present in the dictionary it will return None

2. get( ) �

2. get( ) �

Dictionary Functions and Methods:

• 3. update( ) :
• appends the key-value pair of the dictionary passed as the argument to the key-value pair of the given dictionary

3. update( ) :�

Updated values

Dictionary Functions and Methods:

• 4. keys( ) :Returns a list of keys in the dictionary

Dictionary Functions and Methods:

• 5. values( ) :Returns a list of values in the dictionary

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Ans:1

• 9

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• To see the quiz click me:

Ans: 2

• a=list("PYTHON")
• print(a)
• for x in a:
• print(x)

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• To see the quiz click me:

Ans: 3

• ['p', 'y', 't', 'h', 'o', 'n', 'i', 'x']

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• To see the quiz click me:

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Ans: 4

• ['python', 'i', 'x']

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• To see the quiz click me:

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Ans: 5

• ['python', 'jnv', 'i', 'x', ' ', 'c', 'l', 'a', 's', 's']

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• To see the quiz click me:

Ans: 6

Ans: 7

Ans:7

Ans: 7

Ans:7

Ans: 8

• phonedict={“krishan”:123456,”ram”:321654}
• for name in phonedict:
• print(name,”:”,phonedict[name])

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• krishan : 123456
• ram : 321654

Thank you