List _Python Programming_Built in functions

Copyright © 2021, ABES Engineering College
1
List
.  Python List is the most commonly used sequence.
 Important points about list are as follows.
 List elements are enclosed in square brackets [] and are comma separated.
 List is the sequence of class type ‘list’.
 List can contain elements of different data types.
 List is a mutable(changeable) sequence, would be discussed in detail in 3.2.3
 List allows duplicate elements.
 List elements are ordered, it means it give specific order to the elements, if new element is
added, by default it comes at the end of the list.

2
List
Real World Scenario:
 List is used when there is a
possibility of elements of different
data type.
 For example record of a particular
student, having name as string,
roll.no as integer, marks as float,
father’s name as string.
 To contain this record list is the
appropriate sequence.
List Representation

3
List Example
 In this example a variable named list
example has been created and three
elements have been assigned.
 As we have enclosed elements in
square brackets, this makes list
example is of type list.

4
Ordered Property of List
 Ordered sequence of the list means the
order in which elements appear is
unique
 The position of every element is fixed.
 If we change the position of any element,
then list would not be the same
anymore.

5
Creation of List
Creation of Empty List Creation of Non Empty List
List can be created by many ways as follows.

6
Accessing the List
 In the list index are started from 0, it means first element takes 0 index and it increases like 0,1,2…
(n-1).
 List also supports negative indexing.
 It means last element can be accessed using -1 index, second last as -2 and so on.
Indexing the List

7
Slicing
 Slicing is used to get substring from a string.
 We use Slice operator in the list to get a sub list.
Start= Optional argument by default value
is 0.
End = Optional argument by default value is
number of elements in the list. If any
number given, then value is taken as
number-1.
Step=Options argument by default value is
1.
Colon 1: Required
Colon 2: Optional

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Slicing Example
 Single colon[:]- It is used to print the entire list.
 Double colon[:]- It is used to print the entire list.
 l[2::]-It is used to print the list starting from index 2 till
the last element of the list.
 L[2:5:]- We have set start and end both as 2 and 5,
so it’s starting from 2 and ending with (5-1) and
printing values for indexes 2,3 and 4 index.
 L[2:5:2]-end and step has been set as 2,5 and 2. So
output substring starting from index 2, ending with 5-
1=4 and step counter is 2, so its skipping alternate
element.

9
Examples of List Slicing
Operator Explanation Example
[:] This gives a complete original list
[1:3] It starts with 1th
index and ending
with (3-1=2) index
[2:] Sub list starts with index 2 and
ends at last element as nothing
specified on right side of the
colon

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Examples of List Slicing
Operator Explanation Example
[1:4:] Start=1, stop=4 and by default
step=1.
[1:4:2] Start=1, stop=4 and by step=2.
As the step is 2, it took every 2nd
element.
[::-1] Starting is 0th index and stopping
at last index and step is negative
count so that it would print in
reverse order

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Updation in List:
 List updating involves insertion of new elements, deletion of elements or deletion of complete list.
 List is a mutable sequence it means it allows changes in the elements of list.

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Can you answer these Questions
1.What is the output of the following code?
A.[‘XY’,’YZ’]
B.[‘xy’,’yz’]
C. None of the above
D. Both of the above

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Can you answer these Questions
2.What is the output of the following code?
A. [‘g’,’h’,’k’,’l’,’m’]
B. [‘g’,’h’,’k’,’l’,’m’,9]
C. [‘g’,’h’,’k’,’l’,’m’,8,9]
D. [‘g’,’h’,’k’,’l’,’m’,9,8]

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Add new element in List:
 We can add elements to the existing list using append function.
 Append function always add the element at the end of the list.
Syntax:
Listname.append (element to be added)
In this example element 5 has been
appended in the originally existed list.
It’s being added in the last

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Changing new element in List:
 Value of the element at index 3 has been assigned new value as 5, so element in the output
list is changed from 4 to 5.

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Deletion in List:
List elements can be deleted.
 Using del command If we know the position(index) of the element which is to be deleted.
 We can use the remove method by giving the specific element as given in the example If we know the
position(index) of the element.

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Deletion in List:
 list1 has been deleted and then we are trying to print it and its giving error because
it does not exist now.

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Built in Methods in List
Method Remark Example
len() It calculates the length of the list or the
number of elements in the list.
max(list) It returns the maximum element from the list
min(list) It returns a minimum element from the list
list(seq) It converts into any sequence into a list

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Contd..
Method Remark Example
pop() It deletes the last element from the list
Note – We can also pass index as argument in pop() to
delete a specific index value.
count() It counts the occurrences of a particular element in the list
sort() Sort the elements of the list in ascending order
reverse() Sort the elements of the list in reverse order

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Operations on List
Operation Remark Example
Concatenation Operation adds two list
elements
Repitition
It repeats the list specified
number of times
 Python supports variety of operations on the list

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Contd..
Operation Remark Example
Membership To check whether an element
belongs to the list or not
Membership not I return true of an element
that does not belong to the list
 Python supports variety of operations on the list

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Example
 Write Python Program to swap elements in the list.

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Practice Problems
 Take a list input from user having integer elements and calculate sum and average of the
list.
 Take an input list and swap string elements of the list with empty string.

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Loops with List
 While loop with list  For Loop with list

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Example
 Write a python program to print all positive number of a list.
Practice Exercise:
 Write a python program to remove duplicate from the list.
 Write a python program to count positive, negative and string type elements.

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Nested List
 When we have an element of a list in the form of the list itself, it is called Nested List.
 Elements of the nested list can be accessed using the 2-D indexing access method.
.
In this example, first [1] denotes [3,4] and second [1] represents 4, so it gives output as 4.

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Nested List as a Matrix
 We can represent nested list as matrix also.
 For this we would use nested for loop.
 Outer loop would run for number of elements in the list and inner loop would consider
individual element of the nested list as a list.
.
.

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Example
 Create a flat list from a nested list.
.
.
Practice Exercise:
 Using nested list print transpose, of a given matrix
 Print reverse order of a nested list

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List Comprehensions
.
 Let's suppose we want to write a program to calculate powers of 3 for a given range.
 Python provide us writing iterative programs in much
lesser lines called List comprehension.
 The same problem has been solved using list
comprehension.
 Traditional Programming

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List Comprehension
Syntax:
[ statements for an item in list ]
.
IF ELSE :
 We should notice one change that because in if-else
case output is separated based on the condition.
 if-else and conditions has been written along with
statements.
 We have the facility of adding conditionals in
the list comprehension.

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Can you answer these questions?
1. What will be the Output of the following code?
.
A.[0,1,2,3,4,5]
B.[0,1,2,3,4,5,6]
C.[0,1,2,3]
D. None of the Above

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2. What will be the Output of the following code?
.
A. [5,7,9]
B.[3,4,5]
C.[6,7,8]
D.[9,10,11]

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Tuple
.
 Tuple is an immutable (unchangeable) ordered collection of elements of different data types.
 Generally, when we have data to process, it is not required to modify the data values.
 Take an example of week days, here the days are fixed. So, it is better to store the values in the data
collection, where modification is not required.

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Creation of Tuple
.
Creation of Empty Tuple Creation of Non Empty Tuple
 Syntax of Creating Non Empty Tuple
 In above example, the () round brackets are used
to create the variable of tuple type.
 We can also call the class to create a tuple object
as shown in example below.

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Example
.
 Write a program in python to create one element in tuple
 If you want to create a tuple with single value, it is required to add a comma after the single value as
shown in the above example c=(‘college’,).
 If the comma is not placed, then the single value a= (1) or b=(ABES) will be treated as an
independent value instead of the data collection.

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Packing and Unpacking of Tuple
.
 Tuple can also be created without using parenthesis; it is known as packing.
 Write a program to create tuple without parenthesis.
In above example 1, newtup4=3,4,5,” hello” creates a new tuple without parenthesis.

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Unpacking of Tuple
.
 Write a program to unpack elements in tuple
 Unpacking is called when the multiple variables is assigned to a tuple; then these variables take
corresponding values.
Practice Questions:
 Write a Python program to create the colon of a tuple.
 Write a Python program to unpack a tuple in several variables.

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Accessing Elements in Tuple
.
 Tuple elements can be accessed using indexes, just like String and List .
 Each element in the tuple is accessed by the index in the square brackets [].
 An index starts with zero and ends with (number of elements - 1)
Example:
Write a program to access index 1 element from tuple.
In above example 1: tuple newtup carries multiple types of data in it as “hello” is string, 2 is integer, and
23.45 is float. If we can fetch the index 1 element using print(newtup[1]).

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Contd…
.
 Write a program to access index 0 element from tuple.
 Basically, the -1 index will return the last value of tuple.
 Indexes start from zero, and it goes up to a number of elements or say -1.
 Take another example to fetch the -1 index from tuple.
 last element is accessed by print(tuple_days[-1]).

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Indexing in Tuple and Slicing
.
 Slicing in a tuple is like a list that extracts a part of the tuple from the original tuple.
 Write a program to access elements from 0 to 4 index in tuple.
 Write a program to access elements from 1 to 3 index in tuple.

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Modification/Updating a Tuple
.
 If we want to change any of the index value in tuple, this is not allowed and throw an error.
 Tuple object does not support item assignment.
 Here, we are taking the same above example of days and showing the immutable
characteristic of tuple

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Practice Exercises
.
 Write a Python program to get the 4th element and 4th element from last of a tuple.
 Write a Python program to check whether an element exists within a tuple.

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Quality Content for Outcome based Learning

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Operations on Tuple
.
Tuple has some operations, which are listed below:
Operations Remarks Example
Concatenation Add two tuples
Multiplication
Creates copies of the
tuple
Membership
To check whether an
element belong to tuple
or not
Not Membership
Would return true if
element does not
belong to tuple.

46
Loops and Conditions on Tuples
 In this example The elements are printed while iterating through for loop condition for in tuple_days and then
we print the values of i in each iteration.
 Tuple can be traversed using Loop
 Take the tuple named tuple_days and print all its elements

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Loops and Conditions on Tuples
Example:
 Let have a look to the example where we are placing a condition to return the values
having word length greater than 3.
 In above example , The elements are printed while iterating through for loop condition for in tuple_days
and then we print the values of i in each iteration with the condition if(len(i)>3)

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Practice Exercises:
Exercise: Write Python program to join two input tuples, if their first element is common.

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Dictionaries
 Dictionary is a unique data collection of Python which stores the
key-value pair.
 The user can add an element by giving a user-defined index called a key.
 Each key and its corresponding value makes the key-value pair in dictionary.
 This key-value pair is considered as one item in dictionary.

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Introduction
 In dictionaries, the indexes are not by default. (such as 0 in string,
list, tuple).
 {} is the representation of Dictionary
 Creation of Dictionary
 An empty dictionary can be created as

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Example-1
 Creating an empty dictionary

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Example-2
 Creating a non-empty dictionary

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Accessing of Dictionary
 In dictionary, the items are accessed by the keys.

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1. Output of following code?
A) ‘Java’
B) ‘Python’
C) KeyError
D) None of above

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A) 5
B) 10
C) 15
D) None of above

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Accessing of Dictionary
List
By Default indexing
Indexes are only of
integer type
Adds an element to
the next default
index
Fetching of element
is through index,
lst[0]
Traversing is easy
just by increase the
index, i+=1
Dictionary
User defined Keys
Keys can be of any
type
Adds an element to
the user defined key
location
Fetching of value is
through keys,
dic[<key>]
Traversing is easy
just by increase the
index, i+=1

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Modification in a Dictionary

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A) {1:’Store’,2:’Kitchen’}
B) {2:’Store’,1:’Kitchen’}
C)KeyError
D) None of above

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2. Is it possible to change key in dictionary?
A) True
B) False

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Nested Dictionary
 As we have the option of a nested list, similarly, dictionaries can consist of
data collections.

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Built-in Methods in Dictionary
Method Description
copy() Copying a dictionary to another dictionary
fromkeys() Create a new dictionary with key in a data sequence list/tuple with value
get() If the key is present in the dictionary, its value is returned. If the key is not present in a dictionary, then
the default value will be shown as output instead of a KeyError.
items() this will return the key-value pair as an output.
keys() this will return only the keys as an output.
values() this will return only the dictionary values as an output.
update() this adds the one dictionary with another dictionary.
pop() The pop() method takes an argument as the dictionary key, and deletes the item from the dictionary.
popitem() The popitem() method retrieves and removes the last key/value pair inserted into the
dictionary.

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copy()
 copy() method provide a fresh copy with different memory location.
Output

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fromkey()
Output

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get()
Output

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items(),keys(),values()
Output

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update()
Output

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pop(),popitem()
Output

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Loops and conditions on dictionaries
 Loops and conditions can easily apply to dictionaries.
dict1={1:1,2:4,4:8,6:36}
for key in dict1.keys():
print(key)
for val in dict1.values():
print(val)
for item in dict1.items():
print(item)
for i,j in dict1.items():
print(i,":",j)
OUTPUT
1
2
4
6
1
4
8
36
(1,1)
(2,4)
(4,8)
(6,36)
1:1
2:4
4:8
6:36

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A) {1:1,2:4,3:9,4:16,5:25,6:36}
B) {1:1,2:4,3:9,4:16,5:25}
C) [1,4,9,16,25]
D) Error

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A) {1:’Store’,2:’Kitchen’}
B) {2:’Store’,1:’Kitchen’}
C)KeyError
D) None of above

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Set
 A set is another data collection data types in python, which stores
unique elements in an unordered way.
 Every element in a set is unique and immutable(unchangeable),
i.e. no duplicate values should be there, and the values can’t be
changed.

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Creation of empty Set

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Creation of non-empty Set

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Creation of non-empty Set

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2. Is it possible to create an empty set using like s1={} ?
A) True
B) False

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Accessing set
 Python set’s item cannot be accessed using indexes.

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Built-in Methods in Dictionary
Method Description
copy() Copying a set to another set
clear() Removes all element from set
add() Adding a new item in set
update() If the key is present in the dictionary, its value is returned. If the key is not present in a dictionary, then
the default value will be shown as output instead of a Key Error.
remove() to remove the specified element from the given set.
pop() used to removes a random element from the set and returns the popped (removed) elements.
remove () used to remove the specified element from the given set.
discard () used to remove the specified item from the given input set. the remove() method will give an error if
the specified item does not exist but this method will not.

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copy()
 copy() method provide a fresh copy with different memory location.

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clear()

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add()

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update()

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remove()

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pop()

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discard()

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Operators
Set Operation Description Operator Method
Union All unique elements in set1 and set2 | union()
Intersection Elements present in set1 and set2 & intersection()
Difference
Elements that are present in one set, but not the
other
- difference()
Symmetric Difference Elements present in one set or the other, but not both ^ symmetric_difference()
Disjoint True if the two sets have no elements in common None isdisjoint()
Subset
True if one set is a subset of the other (that is, all
elements of set2 are also in set1)
<= issubset()
Proper Subset
True if one set is a subset of the other,
but set2 and set1 cannot be identical
< None
Superset
True if one set is a superset of the other (that
is, set1 contains all elements of set2)
>= issuperset()
Proper Superset
True if one set is a superset of the other,
but set1 and set2 cannot be identical
> None

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Union

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Intersection

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Intersection

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Set Difference

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Symmetric Difference

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Loops with set

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Frozen Set
A frozen set is a special category of the set which is unchangeable once created

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Frozen Set

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Summary
List Tuple Set Dictionary
List is a collection of values
that is ordered.
Tuple is ordered and
unchangeable collection of
values
Set stores the unique values
as data collection
Dictionary is a collection of
key-value pairs
Represented by [ ] Represented by ( ) Represented by { } Represented by { }
Duplicate elements allowed Duplicate elements allowed Duplicate elements not
allowed
Duplicate keys not allowed, in
dictionary values allowed
duplicate
Values can be of any type Values can be of any type Values can be of any type Keys are immutable type, and
value can be of any type
Example:
[1, 2, 3, 4]
Example:
(1, 2, 3, 4)
Example:
{1, 2, 3, 4}
Example:
{1:1, 2:2, 3:3, 4:4}
List is mutable Tuple is immutable Set is mutable Dictionary is mutable
List is ordered Tuple is ordered Set is unordered Dictionary is insertion
ordered
Creating an empty list
l=list()
l = []
Creating an empty Tuple
t = tuple ()
t=( )
Creating a set
s=set ()
Creating an empty dictionary
d=dict( )
d={}

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1. Which of the following Python code will create a set?
(i) set1=set((0,9,0))
(ii) set1=set([0,2,9])
(iii) set1={}
A) iii
B) i and ii
C) ii and iii
D) All of Above

97
2. What is the output of following code?
set1=set((0,9,0))
print(set1)
A) {0,0,9}
B) {0,9}
C) {9}
D) Error

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3. What is the output of following python code?
set1={1,2,3}
set1.add(4)
set1.add(4)
print(set1)
A) {1,2,3}
B) {1,2,3,4}
C) {1,2,3,4,4}
D) Error

List _Python Programming_Built in functions

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