Python - How To Sort List of Objects in Python

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Python Lists are not homogeneous, which makes them different from the other data types provided in Python.

The indexing of a List starts with 0 as the first index and is done sequentially. All the elements in the list have their definite place because of which duplication is allowed in lists.

This tutorial will introduce different methods to sort the list of objects in Python.

Use the list.sort() Method to Sort the List of Objects in Python

The list.sort() method sorts all the list elements in ascending or descending order.

It contains two optional parameters, key and reverse. The key parameter, just like its name suggests, serves as a key for the sorting process. The reverse parameter is used to determine the sorting order. If the value of reverse is True, then the sorting occurs in reverse/descending order.

However, the function works just fine without the use of the aforementioned optional parameters.

The following code uses the list.sort() method to sort the list of objects in Python.

class BankEMP:       def __init__(self, name, dept, age):         self.name = name         self.dept = dept         self.age = age       def __repr__(self):         return '{' + self.name + ', ' + self.dept + ', ' + str(self.age) + '}'   if __name__ == '__main__':       emps = [         BankEMP('Elijah', 'IT', 20),         BankEMP('Nik', 'Banking', 21),         BankEMP('Lucien', 'Finance', 19)     ]     # sort list by `name` in the natural order     emps.sort(key=lambda x: x.name)     print(emps)       # sort list by `name` in reverse order     emps.sort(key=lambda x: x.name, reverse=True)     print(emps) 

Output:

[{Elijah, IT, 20}, {Lucien, Finance, 19}, {Nik, Banking, 21}] [{Nik, Banking, 21}, {Lucien, Finance, 19}, {Elijah, IT, 20}] 

To produce the value for the key parameter, we can use operator.attrgetter().

attrgetter() is imported from the operator module and is utilized to return a callable object that fetches the attribute from its operand.

The following code uses the list.sort() method and operator.attrgetter() to sort the list of objects in Python.

from operator import attrgetter   class BankEMP:       def __init__(self, name, dept, age):         self.name = name         self.dept = dept         self.age = age       def __repr__(self):         return '{' + self.name + ', ' + self.dept + ', ' + str(self.age) + '}'   if __name__ == '__main__':          emps = [         BankEMP('Elijah', 'IT', 20),         BankEMP('Nik', 'Banking', 21),         BankEMP('Lucien', 'Finance', 19)     ]     #sort list by name in the natural order using 'attrgetter()'      emps.sort(key=attrgetter('name'))       print(emps) 

Output:

[{Elijah, IT, 20}, {Lucien, Finance, 19}, {Nik, Banking, 21}] 

Use the sorted() Function to Sort the List of Objects in Python

Python provides a built-in sorted() function that can serve as an alternative to the list.sort() function.

While list.sort() does not return any specific value and makes changes to the original list, the sorted() function returns the sorted list rather than making any modifications to the original list.

The sorted() function only contains reverse as an optional parameter.

The following code uses the sorted() function to sort the list of objects in Python.

class BankEMP:       def __init__(self, name, dept, age):         self.name = name         self.dept = dept         self.age = age       def __repr__(self):         return '{' + self.name + ', ' + self.dept + ', ' + str(self.age) + '}'   if __name__ == '__main__':          emps = [         BankEMP('Elijah', 'IT', 20),         BankEMP('Nik', 'Banking', 21),         BankEMP('Lucien', 'Finance', 19)     ]          #sort list in natural order of name using sorted() function     sort1= sorted(emps, key=lambda x: x.name)     print(sort1) 

Output:

[{Elijah, IT, 20}, {Lucien, Finance, 19}, {Nik, Banking, 21}]