Skip to main content

Python List Functions & Methods Tutorial and Examples

Learn about Python List functions and methods. Follow code examples for list() and other Python functions and methods now!
Updated Dec 2022  · 7 min read

In Python, you can use a list function which creates a collection that can be manipulated for your analysis. This collection of data is called a list object.

While all methods are functions in Python, not all functions are methods. There is a key difference between functions and methods in Python. Functions take objects as inputs. Methods in contrast act on objects.

Python offers the following list functions:

  • sort(): Sorts the list in ascending order.
  • type(list): It returns the class type of an object.
  • append(): Adds a single element to a list.
  • extend(): Adds multiple elements to a list.
  • index(): Returns the first appearance of the specified value.
  • max(list): It returns an item from the list with max value.
  • min(list): It returns an item from the list with min value.
  • len(list): It gives the total length of the list.
  • list(seq): Converts a tuple into a list.
  • cmp(list1, list2): It compares elements of both lists list1 and list2.
  • filter(fun,list): filter the list using the Python function. 
  • Python List Functions & Methods

Python sort list method

The sort() method is a built-in Python method that, by default, sorts the list in ascending order. However, you can modify the order from ascending to descending by specifying the sorting criteria.

Example

Let's say you want to sort the element in prices in ascending order. You would type prices followed by a . (period) followed by the method name, i.e., sort including the parentheses.

prices = [238.11, 237.81, 238.91]
prices.sort()
print(prices)
[237.81, 238.11, 238.91]

Python list type() function

For the type() function, it returns the class type of an object.

Example

Here we will see what type of both fam and fam2 are:

fam = ["liz", 1.73, "emma", 1.68, "mom", 1.71, "dad", 1.89]
fam
['liz', 1.73, 'emma', 1.68, 'mom', 1.71, 'dad', 1.89]

Let's see what the type of the object is:

type(fam)
list

Now, let's look at fam2.

fam2 = [["liz", 1.73],
        ["emma", 1.68],
        ["mom", 1.71],
        ["dad", 1.89]]
fam2
[['liz', 1.73], ['emma', 1.68], ['mom', 1.71], ['dad', 1.89]]

Let's see what the type of the object is:

type(fam2)
list

These calls show that both fam and fam2 are, in fact, lists.

Python list append method

The append() method will add certain content you enter to the end of the elements you select.

Example

In this example, let's extend the string by adding "April" to the list with the method append(). Using append() will increase the length of the list by 1.

months = ['January', 'February', 'March']
months.append('April')
print(months)

When you run the above code, it produces the following result:

['January', 'February', 'March', 'April']

Python list extend method

The extend() method increases the length of the list by the number of elements that are provided to the method, so if you want to add multiple elements to the list, you can use this method.

Example

x = [1, 2, 3]
x.extend([4, 5])
x

When you run the above code, it produces the following result:

[1, 2, 3, 4, 5]

Python list index method

The index() method returns the first appearance of the specified value.

Example

In the below example, let's look at the index of February in the list months.

months = ['January', 'February', 'March']
prices = [238.11, 237.81, 238.91]
months.index('February')
1

This method helps identify that February is located at index 1. Now we can access the corresponding price of February using this index.

print(prices[1])
237.81

Python list max function

The max() function will return the highest value of the inputted values.

Example

In this example, we will look to use the max() function to find the maximum price in the list named price.

# Find the maximum price in the list price
prices = [159.54, 37.13, 71.17]
price_max = max(prices)
print(price_max)

When you run the above code, it produces the following result:

159.54

Python list min function

The min() function will return the lowest value of the inputted values.

Example

In this example, you will find the month with the smallest consumer price index (CPI).

To identify the month with the smallest consumer price index, you first apply the min() function on prices to identify the min_price. Next, you can use the index method to find the index location of the min_price. Using this indexed location on months, you can identify the month with the smallest consumer price index.

months = ['January', 'February', 'March']
prices = [238.11, 237.81, 238.91]
# Identify min price
min_price = min(prices)

# Identify min price index
min_index = prices.index(min_price)

# Identify the month with min price
min_month = months[min_index]
print[min_month]
February

Python list len function

The len() function shows the number of elements in a list. In the below example, we will look at stock price data again using integers.

Example

stock_price_1 = [50.23]
stock_price_2 = [75.14, 85.64, 11.28]

print('stock_price_1 length is ', len(stock_price_1))
print('stock_price_2 length is ', len(stock_price_2))

When you run the above code, it produces the following result:

stock_price_1 length is 1
stock_price_2 length is 3

Python list() function

The list() function takes an iterable construct and turns it into a list.

Syntax

list([iterable])

Example

In the below example, you will be working with stock price data. Let's print out an empty list, convert a tuple into a list, and finally, print a list as a list.

# empty list
print(list())

# tuple of stock prices
stocks = ('238.11', '237.81', '238.91')
print(list(stocks))

# list of stock prices
stocks_1 = ['238.11', '237.81', '238.91']
print(list(stocks_1))

When you run the above code, it produces the following result:

[]
['238.11', '237.81', '238.91']
['238.11', '237.81', '238.91']

Python cmp function

For the cmp() function, it takes two values and compares them against one another. It will then return a negative, zero, or positive value based on what was inputted.

Example

In the example below, we have two stock prices, and we will compare the integer values to see which one is larger:

stock_price_1 = [50.23]
stock_price_2 = [75.14]

print(cmp(stock_price_1, stock_price_2))
print(cmp(stock_price_1, stock_price_1))
print(cmp(stock_price_2, stock_price_1))

When you run the above code, it produces the following result:

-1
0
1

The results show that the stock_price_2 list is larger than the stock_price_1 list. You can use the cmp() function on any type of list, such as strings. Note that by default, if one list is longer than the other, it will be considered to be larger.

Python filter list function

For the filter() function, it takes a function and the lists and returns an iterator of filtered elements. You can either create a Python filter function or use a lambda function to get a filtered list. 

Note: you can also use loops, list comprehension, and string pattern matching to get a filter list. 

Example

First, we will create a filter function that will return boolean values. It will consist of simple logical functions. In our case, we will filter item prices greater than 350. Then, we will use filter() to apply the function on item_price list and get an iterator of filtered elements. 

To access the filtered elements, we can either extract value using a for loop or convert an iterator into the lists.  

def filter_price(price):
    if (price > 350):
        return True
    else:
        return False
 
item_price = [230, 400, 450, 350, 370]

# applying filter function
filtered_price = filter(filter_price, item_price)


print(list(filtered_price))
[400, 450, 370]

You can also convert your code into a single line using lambda function and get filtered elements. 

# lambda function with filter()
filtered_price = filter(lambda a: a > 350, item_price)
print(list(filtered_price))
[400, 450, 370]

To learn more about list methods and functions, please see this video from our course Introduction to Python for Finance.

This content is taken from DataCamp's Introduction to Python for Finance course by Adina Howe.

Python List Functions & Methods FAQs

What is a list in Python?

One of the main built-in data structures in Python is storing any number of items. The main characteristics of Python lists are that they are iterable, ordered, indexed, mutable, and allow duplicated values.

How to make a list in Python?

Place a sequence of items inside square brackets and separate them by comma, e.g., ['cake', 'ice-cream', 'donut']. Alternatively, use the list() built-in function with double brackets: list(('cake', 'ice-cream', 'donut')). To create an empty list, use empty square brackets ([]) or the list() function without passing any argument (list()). Usually, a Python list is assigned to a variable for further usage.

What is a Python list used for?

When we need to keep together multiple related items placed in a defined order, possibly of heterogeneous data types and/or with duplicates. We then want to be able to modify those items, add or remove items, and apply the same operations on several values at once.

What kinds of objects can a Python list contain?

Any kinds of Python objects, both primitive (integers, floats, strings, boolean) and complex (other lists, tuples, dictionaries, etc.). There can be different data types in one Python list, e.g., ['cake', 1, 3.14, [0, 2]], which makes this data structure very flexible.

Is a Python list ordered?

Yes. The items of a Python list have a fixed order, which makes this data structure also indexed. Each item of a Python list has an index corresponding to its position in the list, starting from 0 for the first item. The last item of a Python list has the index N-1, where N is the number of items in the list.

Is a Python list mutable?

Yes. The values of the items in a Python list can be modified after the list is created, with no need to reassign the list to a variable. The items can also be added or removed, resulting in dynamically changing the size of the list.

Does a Python list allow duplicate values?

Yes. Because these data structures are ordered and indexed, a Python list can contain any number of repeated items.

What is the difference between Python append() and extend()?

While the append() method allows adding a single item at the end of a Python list, the extend() method allows adding multiple items. In the first case, the length of a list is increased by 1; in the second, the length is increased by the number of added items.

About Python

Introduction to Python

Beginner
4 hr
4.7M
Master the basics of data analysis with Python in just four hours. This online course will introduce the Python interface and explore popular packages.
See DetailsRight Arrow
Start Course
See MoreRight Arrow
Related

Precision-Recall Curve in Python Tutorial

Learn how to implement and interpret precision-recall curves in Python and discover how to choose the right threshold to meet your objective.
Vidhi Chugh's photo

Vidhi Chugh

14 min

An Introduction to Hierarchical Clustering in Python

Understand the ins and outs of hierarchical clustering and its implementation in Python
Zoumana Keita 's photo

Zoumana Keita

17 min

Association Rule Mining in Python Tutorial

Uncovering Hidden Patterns in Python with Association Rule Mining
Moez Ali's photo

Moez Ali

14 min

An Introduction to Python Subprocess: Basics and Examples

Explore our step-by-step guide to running external commands using Python's subprocess module, complete with examples.
Moez Ali's photo

Moez Ali

15 min

Setting Up VSCode For Python: A Complete Guide

Experience a simple, fun, and productive way of Python development by learning about VSCode and its extensionsn and features.
Abid Ali Awan's photo

Abid Ali Awan

16 min

GeoPandas Tutorial: An Introduction to Geospatial Analysis

Get started with GeoPandas, one of the most popular Python libraries for geospatial analysis.
Javier Canales Luna's photo

Javier Canales Luna

15 min

See MoreSee More