Returns the largest item

Usage

The max() function can find

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

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

Syntax

max(val1,val2,val3… ,key)

– OR –

max(iterable,key,default)

Find Maximum of Two or More Values

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

x = max(10, 20, 30)
print(x)
# Prints 30

If the values are strings, the string with the highest value in alphabetical order is returned.

x = max('red', 'green', 'blue')
print(x)
# Prints red

Find Maximum in an Iterable

If you specify an Iterable (such as list, tuple, set etc.), the largest item in that iterable is returned.

L = [300, 500, 100, 400, 200]
x = max(L)
print(x)
# Prints 500

If the iterable is empty, a ValueError is raised.

L = []
x = max(L)
print(x)
# Triggers 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.

# Specify default value '0'
L = []
x = max(L, default='0')
print(x)
# Prints 0

Find Maximum with Built-in Function

With optional key parameter, you can specify custom comparison criteria to find maximum value. A key parameter specifies a function to be executed on each iterable’s item before making comparisons.

For example, with a list of strings, specifying key=len (the built-in len() function) finds longest string.

L = ['red', 'green', 'blue', 'black', 'orange']
x = max(L, key=len)
print(x)
# Prints orange

Find Maximum with Custom Function

You can also pass in your own custom function as the key function.

# Find out who is the oldest student
def myFunc(e):
  return e[1]	# return age

L = [('Sam', 35),
    ('Tom', 25),
    ('Bob', 30)]

x = max(L, key=myFunc)
print(x)
# Prints ('Sam', 35)

Find Maximum with lambda

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

# Find out who is the oldest student
L = [('Sam', 35),
    ('Tom', 25),
    ('Bob', 30)]

x = max(L, key=lambda student: student[1])
print(x)
# Prints ('Sam', 35)

Find Maximum of Custom Objects

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

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

# a list of custom objects
L = [Student('Sam', 35),
	Student('Tom', 25),
	Student('Bob', 30)]


x = max(L, key=lambda student: student.age)

print(x)
# Prints ('Sam', 35)