[Tut] list.clear() vs New List — Why Clearing a List Rather Than Creating a New One?

[Tut] list.clear() vs New List — Why Clearing a List Rather Than Creating a New One? - Printable Version

+- Sick Gaming (https://sickgaming.net)
+-- Forum: Programming (https://sickgaming.net/forum-76.html)
+--- Forum: Python (https://sickgaming.net/forum-83.html)
+--- Thread: [Tut] list.clear() vs New List — Why Clearing a List Rather Than Creating a New One? (/thread-98535.html)

[Tut] list.clear() vs New List — Why Clearing a List Rather Than Creating a New One? - xSicKxBot - 11-30-2020

list.clear() vs New List — Why Clearing a List Rather Than Creating a New One?

Problem: You’ve just learned about the

Code:
list.clear()

method in Python. You wonder, what’s its purpose? Why not creating a new list and overwriting the variable instead of clearing an existing list?

Example: Say, you have the following list.

Code:
lst = ['Alice', 'Bob', 'Carl']

If you clear the list, it becomes empty:

Code:
lst.clear()
print(lst)
# []

However, you could have accomplished the same thing by just assigning a new empty list to the variable

Code:
lst

Code:
lst = ['Alice', 'Bob', 'Carl']
lst = []
print(lst)
# []

The output is the same. Why does the

Code:
list.clear()

method exist in the first place?

If you go through the following interactive memory visualizer, you’ll see that both variants lead to different results if you have multiple variables pointing to the list object:

https://pythontutor.com/iframe-embed.html#code=lst_1%20%3D%20%5B'Alice',%20'Bob',%20'Carl'%5D%0Alst_2%20%3D%20lst_1%0Alst_1.clear%28%29%0A%0A%0A%0Alst_1%20%3D%20%5B'Alice',%20'Bob',%20'Carl'%5D%0Alst_2%20%3D%20lst_1%0Alst_1%20%3D%20%5B%5D%0A&codeDivHeight=400&codeDivWidth=350&cumulative=false&curInstr=1&heapPrimitives=nevernest&origin=opt-frontend.js&py=3&rawInputLstJSON=%5B%5D&textReferences=false

In the second example, the variable

Code:
lst_2

still points to a non-empty list object!

So, there are at least two reasons why the

Code:
list.clear()

method can be superior to creating a new list:

Release Memory: If you have a large list that fills your memory—such as a huge data set or a large file read via
Code:
readlines()
—and you don’t need it anymore, you can immediately release the memory with
Code:
list.clear()
. Especially in interactive mode, Python doesn’t know which variable you still need – so it must keep all variables till session end. But if you call
Code:
list.clear()
, it can release the memory for other processing tasks.
Clear Multiple List Variables: Multiple variables may refer to the same list object. If you want to reflect that the list is now empty, you can either call
Code:
list.clear()
on one variable and all other variables will see it, or you must call
Code:
var1 = [], var2 = [], ..., varn = []
for all variables. This can be a pain if you have many variables.

Do you want to develop the skills of a well-rounded Python professional—while getting paid in the process? Become a Python freelancer and order your book Leaving the Rat Race with Python on Amazon (Kindle/Print)!

The post list.clear() vs New List — Why Clearing a List Rather Than Creating a New One? first appeared on Finxter.