built-in methods of list in python
Exploring Essential List Methods in Python
In Python, lists are one of the most commonly used data structures. They are mutable, ordered collections of elements, and offer a wide variety of built-in methods for manipulating and working with list objects. Some of the most commonly used list methods include append(), extend(), insert(), remove(), pop(), index(), count(), sort(), and reverse(). This article provides an overview of these list methods, along with examples of how they can be used in Python code.
Here are the methods :
In Python, a list is an ordered collection of elements, and there are many built-in methods available for manipulating lists. Here is a summary of the most commonly used list methods in Python:
- append(): Adds an element to the end of the list.
- extend(): Adds the elements of a specified list (or any iterable) to the end of the current list.
- insert(): Inserts an element with a value at a specified index position in the list.
- remove(): Removes the first occurrence of an element with a value in the list.
- pop(): Removes and returns the element at a specified index.
- clear(): Removes all elements from the list.
- index(): Returns the index of the first occurrence of an element with a value within a specified range.
- count(): Returns the number of occurrences of an element with a value in the list.
- sort(): Sorts the elements of the list in ascending (or descending) order.
- reverse(): Reverses the order of the elements in the list.
- copy(): Returns a shallow copy of the list.
- len(): Returns the number of elements in the list.
- max(): Returns the maximum element in the list.
- min(): Returns the minimum element in the list.
- sum(): Returns the sum of all elements in the list.
- all(): Returns True if all elements in the list are true (or if the list is empty).
- any(): Returns True if any element in the list is true.
- join(): Concatenates all elements in a list into a single string, with a specified delimiter.
- slice(): Returns a new list that contains a portion of the original list, specified by a start and end index.
- sorted(): Returns a new sorted list (without modifying the original list).
- filter(): Returns a new list containing only the elements for which a specified condition is true (without modifying the original list).
- map(): Returns a new list with the results of applying a function to each element in the original list (without modifying the original list).
These methods make working with lists in Python a powerful and flexible tool for developers.
Here are some examples of built-in methods of lists in Python:
append():
Adds an element to the end of a list.
fruits = ['apple', 'banana', 'cherry']
fruits.append('orange')
print(fruits) # Output: ['apple', 'banana', 'cherry', 'orange']extend():
Adds elements of another list (or any iterable) to the end of the list.
fruits = ['apple', 'banana', 'cherry'] more_fruits = ['orange', 'mango', 'grape'] fruits.extend(more_fruits) print(fruits) # Output: ['apple', 'banana', 'cherry', 'orange', 'mango', 'grape']
insert():
Inserts an element at a specified position in the list.
fruits = ['apple', 'banana', 'cherry'] fruits.insert(1, 'orange') print(fruits) # Output: ['apple', 'orange', 'banana', 'cherry']
remove():
Removes the first occurrence of the specified element from the list.
fruits = ['apple', 'banana', 'cherry']
fruits.remove('banana')
print(fruits) # Output: ['apple', 'cherry']pop():
Removes and returns the element at the specified index (or the last element if no index is specified).
fruits = ['apple', 'banana', 'cherry'] last_fruit = fruits.pop() print(last_fruit) # Output: 'cherry' print(fruits) # Output: ['apple', 'banana']
index():
Returns the index of the first occurrence of the specified element in the list.
fruits = ['apple', 'banana', 'cherry']
index = fruits.index('banana')
print(index) # Output: 1count():
Returns the number of times the specified element appears in the list.
fruits = ['apple', 'banana', 'cherry', 'banana']
count = fruits.count('banana')
print(count) # Output: 2sort():
Sorts the list in ascending order (or descending order if the reverse parameter is set to True).
fruits = ['apple', 'banana', 'cherry'] fruits.sort() print(fruits) # Output: ['apple', 'banana', 'cherry']
reverse():
Reverses the order of the elements in the list.
fruits = ['apple', 'banana', 'cherry'] fruits.reverse() print(fruits) # Output: ['cherry', 'banana', 'apple']
clear():
Removes all elements from the list.
fruits = ['apple', 'banana', 'cherry'] fruits.clear() print(fruits) # Output: []
copy():
Returns a shallow copy of the list.
fruits = ['apple', 'banana', 'cherry'] new_fruits = fruits.copy() print(new_fruits) # Output: ['apple', 'banana', 'cherry']
len():
Returns the number of elements in the list.
fruits = ['apple', 'banana', 'cherry'] count = len(fruits) print(count) # Output: 3
min():
Returns the smallest element in the list.
numbers = [5, 2, 8, 1, 6] smallest = min(numbers) print(smallest) # Output: 1
max():
Returns the largest element in the list.
numbers = [5, 2, 8, 1, 6] largest = max(numbers) print(largest) # Output: 8
any():
Returns True if at least one element in the list is True.
numbers = [0, False, '', [], None] result = any(numbers) print(result) # Output: False
all():
Returns True if all elements in the list are True.
numbers = [1, True, [1, 2], 'hello'] result = all(numbers) print(result) # Output: True
sorted():
Returns a new sorted list from the elements in the original list (the original list remains unchanged).
fruits = ['apple', 'banana', 'cherry'] sorted_fruits = sorted(fruits) print(sorted_fruits) # Output: ['apple', 'banana', 'cherry']
join():
Joins the elements of a list into a string, using a specified separator.
fruits = ['apple', 'banana', 'cherry'] separator = ', ' joined_fruits = separator.join(fruits) print(joined_fruits) # Output: 'apple, banana, cherry'
filter()
is a built-in Python function that is used to filter an iterable (e.g. a list, tuple, or set) based on a given condition. The function takes two arguments: a function that defines the condition to filter on and an iterable to be filtered.
The syntax of filter() is as follows:
filter(function, iterable)
where:
function: A function that returns a Boolean value (i.e. True or False).
This function will be applied to each element in the iterable.
Only the elements for which the function returns True will be included in the output.
iterable: An iterable (e.g. a list, tuple, or set) that you want to filter.
filter() returns a new iterator that contains only the elements from the original iterable for which the function returned True.
Here is an example that demonstrates how to use filter() to remove all even numbers from a list of integers:
# Define the filter function def is_odd(num): return num % 2 != 0 # Define the input list my_list = [1, 2, 3, 4, 5, 6, 7, 8, 9] # Use filter() to remove even numbers from the list filtered_list = list(filter(is_odd, my_list)) # Print the filtered list print(filtered_list) # Output: [1, 3, 5, 7, 9]
In this example, we define the function is_odd() that checks whether a number is odd or not. We then apply this function to each element in the list my_list using filter() to create a new iterator filtered_list that contains only the odd numbers. Finally, we convert the iterator to a list using list(), and print the resulting filtered list.
map()
is a built-in Python function that is used to apply a function to each element of an iterable (e.g. a list, tuple, or set) and return a new iterable with the results.
The syntax of map() is as follows:
map(function, iterable)
where:
function: A function that takes one or more arguments and returns a value. This function will be applied to each element in the iterable.
iterable: An iterable (e.g. a list, tuple, or set) that you want to apply the function to.
map() returns a new iterator that contains the results of applying the function to each element in the original iterable.
Here is an example that demonstrates how to use map() to square each element in a list of integers:
# Define the map function def square(num): return num ** 2 # Define the input list my_list = [1, 2, 3, 4, 5] # Use map() to square each element in the list squared_list = list(map(square, my_list)) # Print the squared list print(squared_list) # Output: [1, 4, 9, 16, 25]
- In this example, we define the function square() that takes a number and returns its square.
- We then apply this function to each element in the list my_list using map() to create a new iterator squared_list that contains the squared values of each element.
- Finally, we convert the iterator to a list using list(), and print the resulting squared list.
Note that the map() function returns an iterator, so we need to convert it to a list or iterate over it to see the results.
sum()
sum() is a built-in Python function that takes an iterable (e.g. a list, tuple, or set) and returns the sum of all the elements in the iterable. If the iterable contains non-numeric values, a TypeError is raised.
The syntax of sum() is as follows:sum(iterable, start=0)
where:
iterable: An iterable (e.g. a list, tuple, or set) that you want to sum.
start (optional): A numeric value that is added to the sum of the iterable. The default value is 0.
sum() returns the sum of all the elements in the iterable, plus the value of start if it is provided.
Here is an example that demonstrates how to use sum() to find the sum of all the elements in a list of integers:
# Define the input list my_list = [1, 2, 3, 4, 5] # Use sum() to find the sum of the list sum_of_list = sum(my_list) # Print the sum of the list print(sum_of_list) # Output: 15
In this example, we define the list my_list that contains five integers. We then use sum() to find the sum of the list, which is 15. Finally, we print the sum of the list.
Note that sum() can also be used to find the sum of elements in a list of floats or other numeric types, as well as nested lists (if the inner lists are also numeric). However, if the iterable contains non-numeric values,a TypeError will be raised.
Quiz: Built-in Methods of Lists in Python
Question 1:
What does the append() method do?
a) Removes an element from the end of the list.
b) Adds an element to the end of the list.
c) Reverses the order of elements in the list.
d) Sorts the elements of the list.
Question 2:
How can you add the elements of another list to the end of the current list?
a) Using insert() method.
b) Using append() method.
c) Using extend() method.
d) Using add() method.
Question 3:
What does the remove() method do?
a) Removes all elements from the list.
b) Removes the first occurrence of an element with a specified value.
c) Removes and returns the element at a specified index.
d) Reverses the order of the elements in the list.
Question 4:
Which method is used to remove and return the last element of a list?
a) remove()
b) pop()
c) clear()
d) delete()
Question 5:
What is the purpose of the sort() method?
a) Removes the last element from the list.
b) Sorts the elements of the list in ascending order.
c) Reverses the order of the elements in the list.
d) Returns a shallow copy of the list.
Question 6:
How can you find the index of the first occurrence of an element in a list?
a) Using index() method.
b) Using find() method.
c) Using search() method.
d) Using locate() method.
Question 7:
What does the len() method return?
a) The largest element in the list.
b) The number of elements in the list.
c) The smallest element in the list.
d) The sum of all elements in the list.
Question 8:
Which method is used to create a shallow copy of a list?
a) copy()
b) clone()
c) duplicate()
d) replicate()
Question 9:
What is the purpose of the all() method?
a) Returns True if at least one element in the list is true.
b) Returns True if all elements in the list are true.
c) Returns the sum of all elements in the list.
d) Joins the elements of a list into a single string.
Question 10:
How can you join the elements of a list into a string with a specified delimiter?
a) Using concat() method.
b) Using merge() method.
c) Using join() method.
d) Using combine() method.
Bonus Question:
Explain the purpose of the filter() and map() methods in Python lists.
Answers:
1-b) Adds an element to the end of the list.
2-c) Using extend() method.
3-b) Removes the first occurrence of an element with a specified value.
4-b) pop()
5-b) Sorts the elements of the list in ascending order.
6-a) Using index() method.
7-b) The number of elements in the list.
8-a) copy()
9-b) Returns True if all elements in the list are true.
10-c) Using join() method.
Bonus Answer:
filter() is used to filter elements from an iterable based on a given condition, and map() is used to apply a function to each element of an iterable, creating a new iterable with the results.