Usage of python function

Question

I'm a new learner of python/programming. Here is a question on top of head about the use of function in python.

If I had a list called myList.

(a) If I were to sort it, I would use myList.sort()
(b) If I were to sort it temporarily, I would use sorted(myList)

Note the difference between the use of two functions, one is to apply the function to myList, the other one is use myList as a parameter to the function.

My question is, each time when I use a function.

How do I know if the function should be used as an "action" to be applied to an object (in (a)), or
should an object passed to the function as a parameter,(in (b)).

I have been confused with this for quite long time. appreciate any explanations.

Thanks.

myList.sort() is a method, but sorted(myList) is a function — Druta Ruslan
– Druta Ruslan, Commented Jul 6, 2018 at 12:55
list.sort and sorted are two entirely different things. One is a method, the other a builtin function. It's not like any function can be used either as foo(x) or x.foo(). — tobias_k
– tobias_k, Commented Jul 6, 2018 at 13:26

Ketan Mukadam · Accepted Answer · 2018-07-06 13:03:25Z

2

There are two big differences between list.sort and sorted(list)

The list.sort() sorts the list in-place, which means it modifies the list. The sorted function does not modify original list but returns a sorted list
The list.sort() only applies to list (it is a method), but sorted built-in function can take any iterable object.

Please go through this useful documentation.

answered Jul 6, 2018 at 13:03

Ketan Mukadam

8694 silver badges7 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

MisterMiyagi · Accepted Answer · 2018-07-06 13:44:36Z

Only sorted is a function - list.sort is a method of the list type.

Functions such as sorted are applicable to more than a specific type. For example, you can get a sorted list, set, or even a temporary generator. Only the output is concrete (you always get a new list) but not the input.

Methods such as sort are applicable only to the type that holds them. For example, there is a list.sort method but not a dict.sort method. Even for types whose methods have the same name, switching them is not sensible - for example, set.copy cannot be used to copy a dict.

An easy way to distinguish the two is that functions live in regular namespaces, such as modules. On the other hand, methods only live inside classes and their instances.

sorted     # function
list.sort  # method

import math
math.sqrt                # function
math.pi.as_integer_ratio # method

Conventionally, Python usually uses functions for immutable actions and methods for mutating actions. For example, sorted provides a new sorted list leaving the old one untouched; my_list.sort() sorts the existing list, providing no new one.

my_list = [4, 2, 3, 1]
print(sorted(my_list))  # prints [1, 2, 3, 4]
print(my_list)          # prints [4, 2, 3, 1] - unchanged by sorted
print(my_list.sort())   # prints None - no new list produced
print(my_list)          # prints [1, 2, 3, 4] - changed by sort

vielkind · Accepted Answer · 2018-07-06 13:02:33Z

1

sort() is an in-place function whereas sorted() will return a sorted list, but will not alter your variable in place. The following demonstrates the difference:

l = [1, 2, 1, 3, 2, 4]
l.sort()
print(l) --returns [1, 1, 2, 2, 3, 4]

l = [1, 2, 1, 3, 2, 4]
new_l = sorted(l) 
print(new_l) -- returns [1, 1, 2, 2, 3, 4]
print(l) -- [1, 2, 1, 3, 2, 4]

If you want to maintain the original order of your list use sorted, otherwise you can use sort().

answered Jul 6, 2018 at 13:02

vielkind

2,9801 gold badge19 silver badges17 bronze badges

Collectives™ on Stack Overflow

Usage of python function

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related