Python max() Function

The max() function returns:

• the largest of two or more vales (such as numbers, strings, etc.)
• the largest item in an iterable (such as list, tuple etc.)

note

With optional key parameter, you can specify custom comparison criteria to find maximum value.

Syntax for two or more values

max(val1, val2, val... ,key)

max() Parameters

Python max() function parameters:

Parameter	Condition	Description
val1,val2,val3...	Required	Two or more values to compare
key	Optional	A function to specify the comparison criteria. Default value is None.

max() Return Value

Python max() function returns the largest element.

danger

You have to specify minimum two values to compare. Otherwise, TypeError exception is raised.

Syntax for iterables

max(iterable, key, default)

max() Parameters

Python max() function parameters:

Parameter	Condition	Description
iterable	Required	Any iterable, with one or more items to compare
key	Optional	A function to specify the comparison criteria. Default value is None.
default	Optional	A value to return if the iterable is empty. Default value is False.

max() Return Value

Python max() function returns the largest item in the iterable.

danger

If the iterable is empty, a ValueError is raised.

To avoid such exception, add default parameter. The default parameter specifies a value to return if the provided iterable is empty.

Examples

Example 1: Get the largest String with max() function

The max() function compares the strings lexicographically (i.e., it compares the strings character by character from left to right, alphabetically). The first string where a character is lexicographically greater than the corresponding character in the other string is returned as the maximum.

str1 = "Tutorial"
str2 = "Reference"
str3 = "for"
str4 = "you!"

max_val = max(str1, str2, str3, str4)
print(max_val)  # Output: 'you!'

output

you!

Notice that the example returns you! because it is the string that comes last in lexicographical order among the provided strings

Another example:

str1 = "aaa"
str2 = "aaaa"
str3 = "AAA"
str4 = "AAAA"

max_val = max(str1, str2, str3, str4)
print(max_val)  # Output: 'aaaa'

output

aaaa

Example 2: Get the largest string with max() function and key parameter

You can specify the comparison criteria by using the key parameter of the max() function.

For example, we can get the longest string by specifying the function len for the key parameter:

str1 = "Tutorial"
str2 = "Reference"
str3 = "for"
str4 = "you!"

max_val = max(str1, str2, str3, str4, key=len)
print(max_val)  # Output: 'Reference'

output

Reference

Example 3: Get the maximum number of two or more values

If you specify two or more values, the largest value is returned.

x = max(10, 20, 30)
print(x) # Output: 30

output

30

Example 4: Get the maximum item in a List

For example, get the maximum number from a list of numbers:

number = [3, 2, 8, 5, 10, 6]
largest_number = max(number)

print(largest_number) # Output: 10

output

10

For example, get the largest string (ordered alphabetically) from a list of strings:

languages = ["Python", "Java", "JavaScript", "Rust"]
largest_string = max(languages)
print(largest_string) # Output: Rust

output

Rust

Example 5: use max() function with dictionary

In the case of dictionaries, max() returns the largest key.

Let's use the key parameter in the max() function to find the dictionary key that is associated with the highest value.

square = {2: 4, -3: 9, -1: 1, -2: 4}

# the largest key
key1 = max(square)
print("The largest key:", key1)    # Output: 2

# the key whose value is the largest
key2 = max(square, key = lambda k: square[k])

print("The key with the largest value:", key2)    # Output: -3

# getting the largest value
print("The largest value:", square[key2])    # Output: 9

output

The largest key: 2
The key with the largest value: -3
The largest value: 9

Observe that:

• The second max() function use the lambda function passed to the key parameter.

Example 6: empty iterable and max() function

If the iterable is empty, a ValueError is raised.

my_list = []
x = max(my_list) # Triggers ValueError: max() arg is an empty sequence
print(x) 

output

Traceback (most recent call last):
  File "main.py", line 2, in <module>
    x = max(my_list) # Triggers ValueError: max() arg is an empty sequence
ValueError: max() arg is an empty sequence

To avoid such exception, add default parameter. The default parameter specifies a value to return if the provided iterable is empty.

If the iterable is empty, a ValueError is raised.

my_list = []
x = max(my_list, default='0')
print(x) 

output

0

Example 7: Find Maximum with Custom Function

You give a user-defined function as key parameter of max() function for making comparisons:

For example, find out who is the oldest student in the given list of students:

def myFunc(elem):
  return elem[1]	# return age

students = [('Ryan', 35), ('Tom', 25), ('Charlie', 30)]

oldest_one = max(students, key=myFunc)
print(oldest_one) # Output: ('Ryan', 35)

output

('Ryan', 35)

Example 8: Find Maximum with lambda

A key function may also be created with the lambda expression. It allows us to in-line function definition.

As in the example7, find out who is the oldest student in the given list of students:

def myFunc(elem):
  return elem[1]	# return age

students = [('Ryan', 35), ('Tom', 25), ('Charlie', 30)]

oldest_one = max(students, key=lambda student: student[1])
print(oldest_one) # Output: ('Ryan', 35)

output

('Ryan', 35)

Example 9: Find Maximum of Custom Objects

Now, let’s create a list of students (as a custom object) and find out who is the oldest student.

class Student:
	def __init__(self, name, age):
		self.name = name
		self.age = age
	def __repr__(self):
		return repr((self.name, self.age))

students = [Student('Ryan', 35), Student('Tom', 25), Student('Charlie', 30)]

oldest_one = max(students, key=lambda student: student.age)
print(oldest_one) # Output: ('Ryan', 35)

output

('Ryan', 35)