Python Sort Class Object List – with Python sorted()

In the post, we show how to use Python sorted() built-in function to sort a Python object list.

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Python sorted() built-in

sorted() builds a new sorted list from an iterable.

Method signature ->

sorted(iterable, *, key=None, reverse=False)

Example:

>>> sorted([10, 6, 3, 2, 7])
[2, 3, 6, 7, 10]

Python Class & Object List

– Define Python class:

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

– Python Object List:

>>> customer_objects = [
...     Customer('Peter', 24),
...     Customer('Mary', 18),
...     Customer('Jack', 42),
... ]

Python Sort

Using Key Function

sorted() uses a key parameter to specify a called function on each list element prior to making comparisons.

>>> sorted(customer_objects, key=lambda customer:customer.age)
[('Mary', 18), ('Peter', 24), ('Jack', 42)]
Using Operator Function

Python provides operator module has itemgetter(), attrgetter(), and a methodcaller() function.
For sorting with objects list, we can use attrgetter() function ->

>>> from operator import attrgetter
>>>
>>> sorted(customer_objects, key=attrgetter('age'))
[('Mary', 18), ('Peter', 24), ('Jack', 42)]
Ascending and Descending

– Use reverse parameter with a boolean value.

  • case reverse = False (default) -> Ascending Sorting
  • case reverse = True -> Descending Sorting
>>> sorted(customer_objects, key=lambda customer:customer.age, reverse=True)
[('Jack', 42), ('Peter', 24), ('Mary', 18)]

or

>>> sorted(customer_objects, key=attrgetter('age'), reverse=True)
[('Jack', 42), ('Peter', 24), ('Mary', 18)]


By grokonez | July 16, 2018.

Last updated on December 20, 2018.



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