[Tut] Python List max()

Python List max()

Do you want to find the maximum of a Python list? This article gives you everything you need to know to master the max() function in Python.

Description

Python’s built-in max() function returns the maximum element of a list or its generalization (an iterable).

Syntax

The syntax of the max() function is as follows:

max(list, default=obj, key=func)

Arguments

Argument	Description
list	The list or iterable from which you get the maximum value.
default	If the iterable is empty, returns this default object.
key	A function that associated a weight to each element in the iterable based on which the maximum is calculated.

Return Value

The return value of the max(list) function is a single element from the list that is the maximum of all elements. If the list is empty, the default object is returned, if explicitly defined. If not, a ValueError is thrown.

Examples

Let’s consider four examples that show how the arguments play together:

Exercise: Guess the output of the four print statements in the code. Run the code. How many did you guess right?

Maximum of List of Lists

Original article: How to Find the Maximum of a List of Lists?

To find the maximal list in a list of lists, you need to make two lists comparable. How? With the key argument of the max() function. The key argument is a function that takes one input (a list) and returns one output (a numerical value). The list with the largest numerical value is returned as the maximum of the list of lists.

Problem: Say you have a list of lists (nested list) and you want to find the maximum of this list. It’s not trivial to compare lists—what’s the maximum among lists after all? To define the maximum among the inner lists, you may want to consider different objectives.

1. The first element of each inner list.
2. The i-th element of each inner list.
3. The sum of inner list elements.
4. The maximum of inner list elements.
5. The minimum of inner list elements.

Example: Given list of lists [[1, 1, 1], [0, 2, 0], [3, 3, -1]]. Which is the maximum element?

1. The first element of each inner list. The maximum is [3, 3, -1].
2. The i-th element of each inner list (i = 2). The maximum is [1, 1, 1].
3. The sum of inner list elements. The maximum is [3, 3, -1].
4. The maximum of inner list elements. The maximum is [3, 3, -1].
5. The minimum of inner list elements. The maximum is [3, 3, -1].

So how do you accomplish this?

Solution: Use the max() function with key argument.

Let’s study the solution code for our different versions of calculating the maximum “list” of a list of lists (nested list).

lst = [[1, 1, 1], [0, 2, 0], [3, 3, -1]] # Maximum using first element

print(max(lst, key=lambda x: x[0]))

# [3, 3, -1] # Maximum using third element

print(max(lst, key=lambda x: x[2]))

# [1, 1, 1] # Maximum using sum()

print(max(lst, key=sum))

# [3, 3, -1] # Maximum using max

print(max(lst, key=max))

# [3, 3, -1] # Maximum using min

print(max(lst, key=min))

# [1, 1, 1]

Try it yourself in our interactive code shell:

Related articles:

• How to Find the Maximum of a List of Lists in Python?
• How to Find the Minimum of a List of Lists in Python?
• Python List Methods [Overview]
• Python List sort() – The Ultimate Guide
• Python Lists – Everything You Need to Know to Get Started
• Key with Maximum Value in Dict

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