List and Functions Reading Material

 

1. What are the Data Structures?

Data Structures allow us to store and organize data efficiently. This will allow us to easily access and perform operations on the data.

In Python, there are four built-in data structures

• List
• Tuple
• Set
• Dictionary

2. What is a list?

The List is the most versatile python data structure that holds an ordered sequence of items.

Creating a List

A List can be created by enclosing elements within [square] brackets where each item is separated by a comma.

Code

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a = 2

list_a = [5, "Six", a, 8.2]

print(type(list_a))

print(list_a)

PYTHON

Output

<class 'list'>

[5, 'Six', 2, 8.2]

3. Explain a few List Methods?

Append

Adds an element to the end of the list.

Syntax

list.append(value)

Code

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list_a = []

for x in range(1, 4):

list_a.append(x)

print(list_a)

PYTHON

Output

[1, 2, 3]

Extend

Adds all the elements of a sequence to the end of the list.

Syntax

list_a.extend(list_b)

Code

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list_a = [1, 2, 3]

list_b = [4, 5, 6]

list_a.extend(list_b)

print(list_a)

PYTHON

Output

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

Insert

Inserts the given element at the specified index.

Syntax

list.insert(index, value)

Code

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list_a = [1, 2, 3]

list_a.insert(1, 4)

print(list_a)

PYTHON

Output

[1, 4, 2, 3]

Pop

Removes the last item from the list.

Syntax

list.pop()

Code

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list_a = [1, 2, 3]

list_a.pop()

print(list_a)

PYTHON

Output

[1, 2]

Remove

Removes the first matching element from the list.

Syntax

list.remove(value)

Code

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list_a = [1, 3, 2, 3]

list_a.remove(3)

print(list_a)

PYTHON

Output

[1, 2, 3]

Clear

Removes all the items from the list.

Syntax

list.clear()

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list_a = [1, 2, 3]

list_a.clear()

print(list_a)

PYTHON

Output

[]

Index

Returns the index of the first occurrence of the specified item in the list.

Syntax

list.index(item)

Code

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list_a = [1, 3, 2, 3]

index = list_a.index(3)

print(index)

PYTHON

Output

1

Count

Returns the number of elements with the specified value.

Syntax

list.count(value)

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list_a = [1, 2, 3]

count = list_a.count(2)

print(count)

PYTHON

Output

1

Sort

Sorts the items of a list in ascending ascending order. The

sort()

method modifies the original list.

Syntax

list.sort()

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list_a = [1, 3, 2]

list_a.sort()

print(list_a)

PYTHON

Output

[1, 2, 3]

Sorted

Sorts the items of a list in ascending ascending order. The

sorted()

method returns the modified list.

Syntax

sorted()

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list_a = [1, 3, 2]

list_b = sorted(list_a)

print(list_b)

PYTHON

Output

[1, 2, 3]

Code

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list_a = [1, 3, 2]

sorted(list_a)

print(list_a)

PYTHON

Output

[1, 3, 2]

4. What is the difference between 

append()

 and 

extend()

?

append	extend
.append() takes a single element as an argument	.extend() takes an iterable as an argument (list, tuple, dictionaries, sets, strings)
.append() adds a single element to the end of the list	.extend() can add multiple individual elements to the end of the list

5. How to use the 

split()

 method?

The

split()

splits a string into a list at every specified separator.

Syntax:

str_var.split(separator)

Example

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nums = "1 2 3 4"

num_list = nums.split()

print(num_list)

PYTHON

Output

['1', '2', '3', '4']

If no separator is specified, the default separator is whitespace.

Using separator

Example

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nums = "1,2,3,4"

num_list = nums.split(',')

print(num_list)

PYTHON

Output

['1', '2', '3', '4']

6. How to use the 

join()

 method?

The

join()

takes all the items in a sequence of strings and joins them into one string.

Syntax:

str.join(sequence)

Example

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list_a = ['Python is ', ' progr', 'mming l', 'ngu', 'ge']

string_a = "a".join(list_a)

print(string_a)

PYTHON

Output

Python is a programming language

7. What is List Slicing?

Obtaining a part of a list is called List Slicing.

Syntax:

variable_name[start_index:end_index]

• end_index
   is not included in the slice.

Code

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list_a = [5, "Six", 2, 8.2]

list_b = list_a[:2]

print(list_b)

PYTHON

Output

[5, 'Six']

Extended Slicing

Similar to string extended slicing, we can extract alternate items from the list using the step.

Syntax:

variable[start_index:end_index:step]

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list_a = ["R", "B", "G", "O", "W"]

list_b = list_a[0:5:3]

print(list_b)

PYTHON

Output

['R', 'O']

8. What is Negative Indexing?

Using a negative index returns the nth item from the end of the list.

The last item in the list can be accessed with the index

-1

Accessing List Items with Negative Index

Example-1

Code

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list_a = [5, 4, 3, 2, 1]

item = list_a[-1]

print(item)

PYTHON

Output

1

Example-2

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list_a = [5, 4, 3, 2, 1]

item = list_a[-4]

print(item)

PYTHON

Output

4

Slicing With Negative Index

You can also specify negative indices while slicing a List.

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list_a = [5, 4, 3, 2, 1]

list_b = list_a[-3:-1]

print(list_b)

PYTHON

Output

[3, 2]

Out of Bounds Index

While slicing, the index can go beyond the size of the list.

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list_a = [5, 4, 3, 2, 1]

list_b = list_a[-6:-2]

print(list_b)

PYTHON

Output

[5, 4, 3]

9. How to reverse a List?

Reversing a list using

reverse()

method:

The

reverse()

method can be used to reverse a List. It updates the original list.

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week_days = ['Monday', 'Tuesday', 'Wednesday']

week_days.reverse()

print(week_days)

PYTHON

Output

['Wednesday', 'Tuesday', 'Monday']

Reversing a list using list slicing:

A list can be reversed using extended slicing.

Syntax:

variable[start:end:negative_step]

-1

for step will reverse the order of items in the list.

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list_a = [5, 4, 3, 2, 1]

list_b = list_a[::-1]

print(list_b)

PYTHON

Output

[1, 2, 3, 4, 5]

10. Explain about functions in Python?

A function is a block of reusable code to perform a specific action. Functions help us in using existing code without writing it every time we need it.

A function can be defined using a keyword

def

. A function is uniquely identified by the

function_name

.

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def greet():

print("Hello")

greet()

greet()

PYTHON

Output

Hello

Hello

Function Arguments

We can pass values to a function using Argument.

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def greet(word):

msg = "Hello " + word

print(msg)

name1 = input()

name2 = input()

greet(word = name1)

greet(word = name2)

PYTHON

Input

Teja

Rahul

Output

Hello Teja

Hello Rahul

Providing default values

Default values indicate that the function argument will take that value if no argument value is passed during the function call.

Example

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def greet(arg_1 = "Hi", arg_2 = "Ram"):

print(arg_1 + " " + arg_2)

greeting = input()

name = input()

greet()

PYTHON

Input

Hello

Teja

Output

Hi Ram

11. What is Recursion?

A function calling itself is called Recursion

Let's understand recursion with a simple example of multiplying N numbers

Multiply N Numbers

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def factorial(n): # Recursive Function

if n == 1: # Base Case

return 1

return n * factorial(n - 1) # Recursion

num = int(input())

result = factorial(num)

print(result)

PYTHON

Input

5

Output