What is list and explain list methods?

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list and list methods

List
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List :

The Python List is a general data structure widely used in Python programs. They are found in other languages,

often referred to as dynamic arrays. They are both mutable and a sequence data type that allows them to be indexed

and sliced.

The list can contain different types of objects, including other list objects.


List methods and supported operators :


Starting with a given list a :


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


1.append(value) – appends a new element to the end of the list. 


# Append values 6, 7, and 7 to the list
a.append(6)
a.append(7)
a.append(7)
# a: [1, 2, 3, 4, 5, 6, 7, 7]
# Append another list
b = [8, 9]
a.append(b)
# a: [1, 2, 3, 4, 5, 6, 7, 7, [8, 9]]
# Append an element of a different type, as list elements do not need to have the same type
my_string = "hello world"
a.append(my_string)
# a: [1, 2, 3, 4, 5, 6, 7, 7, [8, 9], "hello world"]


Note that the append() method only appends one new element to the end of the list. If you append a list to

another list, the list that you append becomes a single element at the end of the first list.


# Appending a list to another list
a = [1, 2, 3, 4, 5, 6, 7, 7]
b = [8, 9]
a.append(b)
# a: [1, 2, 3, 4, 5, 6, 7, 7, [8, 9]]
a[8]
# Returns: [8,9]


2.extend(enumerable) – extends the list by appending elements from another enumerable.


a = [1, 2, 3, 4, 5, 6, 7, 7]
b = [8, 9, 10]
# Extend list by appending all elements from b
a.extend(b)
# a: [1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 10]
# Extend list with elements from a non-list enumerable:
a.extend(range(3))
# a: [1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 10, 0, 1, 2]

Lists can also be concatenated with the + operator. Note that this does not modify any of the original lists:

a = [1, 2, 3, 4, 5, 6] + [7, 7] + b
# a: [1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 10]

a = [1, 2, 3, 4, 5, 6] + [7, 7] + b

# a: [1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 10]


3.index(value, [startIndex]) – gets the index of the first occurrence of the input value.


If the input value is not in the list a ValueError exception is raised. If a second argument is provided, the search is started at that specified index.


a.index(7)
# Returns: 6
a.index(49) # ValueError, because 49 is not in a.
a.index(7, 7)
# Returns: 7
a.index(7, 8) # ValueError, because there is no 7 starting at index 8


4.insert(index, value) – inserts value just before the specified index .

Thus after the insertion the new element occupies position index .


a.insert(0, 0) # insert 0 at position 0
a.insert(2, 5) # insert 5 at position 2
# a: [0, 1, 5, 2, 3, 4, 5, 6, 7, 7, 8, 9, 10]

.

5.pop([index]) – removes and returns the item at index .

With no argument it removes and returns the last element of the list.

a.pop(2)
# Returns: 5
# a: [0, 1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 10]
a.pop(8)
# Returns: 7
# a: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
# With no argument:
a.pop()
# Returns: 10
# a: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]


6.remove(value) – removes the first occurrence of the specified value.


If the provided value cannot be found, a ValueError is raised.

a.remove(0)
a.remove(9)
# a: [1, 2, 3, 4, 5, 6, 7, 8]
a.remove(10)
# ValueError, because 10 is not in a


7.reverse() – reverses the list in-place and returns None


a.reverse()
# a: [8, 7, 6, 5, 4, 3, 2, 1]


There are also other ways of reversing a list.


8.count(value) – counts the number of occurrences of some value in the list.


a.count(7)
# Returns: 2


9.sort() – sorts the list in numerical and lexicographical order and returns None.


a.sort()
# a = [1, 2, 3, 4, 5, 6, 7, 8]
# Sorts the list in numerical order


Lists can also be reversed when sorted using the reverse=True flag in the sort() method.


a.sort(reverse=True)
# a = [8, 7, 6, 5, 4, 3, 2, 1]

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