Sort a list of objects by multiple attributes in Python

This post will discuss how to sort a list of objects by multiple attributes in Python.

In the previous post, we have seen how to sort a list of objects using a single attribute. This post will discuss how to sort a list of objects using multiple attributes in Python.

1. Using `list.sort()` function

A Pythonic solution to in-place sort a list of objects using multiple attributes is to use the list.sort() function. It accepts two optional keyword-only arguments: key and reverse and produces a stable sort. The key specifies a function of one argument to extract a comparison key from each list item, and the list will be sorted in reversed order when the reverse is True.

To illustrate, the following sorts a list of Employee object with some attributes sorted in the natural order, and remaining attributes sorted in the reverse order.

class Associate:

def __init__(self, name, dept, salary):

self.name = name

self.dept = dept

self.salary = salary

def __repr__(self):

return '{' + self.name + ', ' + self.dept + ', ' + str(self.salary) + '}'

if __name__ == '__main__':

associates = [

Associate('James', 'Finance', 80000),

Associate('Robert', 'Construction', 60000),

Associate('James', 'Telecom', 70000)

]

# 1. Sort by only `dept` attribute

associates.sort(key=lambda x: x.dept)

# [{Robert, Construction, 60000}, {James, Finance, 80000}, {James, Telecom, 70000}]

print(associates)

# 2. Sort by `name` attribute, followed by `dept` attribute

associates.sort(key=lambda x: (x.name, x.dept))

# [{James, Finance, 80000}, {James, Telecom, 70000}, {Robert, Construction, 60000}]

print(associates)

# 3. Sort by `name` attribute in reverse order,

#, followed by `dept` attribute in reverse order

associates.sort(key=lambda x: (x.name, x.dept), reverse=True)

# [{Robert, Construction, 60000}, {James, Telecom, 70000}, {James, Finance, 80000}]

print(associates)

# 4. Sort by `name` attribute in the natural order,

#, followed by numeric `salary` attribute in reverse order

associates.sort(key=lambda x: (x.name, -x.salary))

# [{James, Finance, 80000}, {James, Telecom, 70000}, {Robert, Construction, 60000}]

print(associates)

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If you don’t need any attributes sorted in reverse order, consider using the attrgetter() function from the operator module to produce the key.

from operator import attrgetter

class Associate:

def __init__(self, name, dept):

self.name = name

self.dept = dept

def __repr__(self):

return '{' + self.name + ', ' + self.dept + '}'

if __name__ == '__main__':

associates = [

Associate('James', 'Telecom'),

Associate('Robert', 'Construction'),

Associate('James', 'Finance')

]

# sort by `name` and `dept` attribute

associates.sort(key=attrgetter('name', 'dept'))

# [{James, Finance}, {James, Telecom}, {Robert, Construction}]

print(associates)

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2. Using `sorted()` function

The list.sort() function modifies the list in-place. To return a new sorted list instance, you can use the sorted() built-in. It accepts the same keyword-only arguments as the list.sort() function.

class Associate:

def __init__(self, name, dept):

self.name = name

self.dept = dept

def __repr__(self):

return '{' + self.name + ', ' + self.dept + '}'

if __name__ == '__main__':

associates = [

Associate('James', 'Telecom'),

Associate('Robert', 'Construction'),

Associate('James', 'Finance')

]

# sort by `name` and `dept` attribute

sortByNameAndDept = sorted(associates, key=lambda x: (x.name, x.dept))

# [{James, Finance}, {James, Telecom}, {Robert, Construction}]

print(sortByNameAndDept)

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That’s all about sorting a list of objects by multiple attributes in Python.

Sort a list of objects by multiple attributes in Python

1. Using list.sort() function

2. Using sorted() function

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1. Using `list.sort()` function

2. Using `sorted()` function