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![Ben Slivinn](https://uploads.teamtreehouse.com/production/profile-photos/5037232/micro_Ben.jpg)
Ben Slivinn
10,156 PointsCould you please explain why are we using self = str.__new__(*args)?
Object-Oriented Python, Subclassing Built-ins.
I tried to play with ReversedStr's new() method and add a loop to accept multiple arguments (rs = ReversedStr(321, 987), and the first argument successfully converted to string type because of str.new() (In my understanding its because str.new()), but the second one isn't. That is when I understood that I don't really get it why you are using str.new().
Sourcecode:
class ReverseStr(str):
def __new__(*args):
self = str.__new__(*args) # self is just a variable name.
self = self[::-1]
return self
rs = ReverseStr(321)
print(rs)
Thank you!
1 Answer
![Chris Freeman](https://uploads.teamtreehouse.com/production/profile-photos/1153532/micro_image.jpg)
Chris Freeman
Treehouse Moderator 68,425 PointsGreat question!
From https://mail.python.org/pipermail/tutor/2008-April/061426.html:
Use __new__
when you need to control the creation of a new instance.
Use __init__
when you need to control initialization of a new instance.
__new__
is the first step of instance creation. It's called first,
and is responsible for returning a new instance of your class. In
contrast, __init__
doesn't return anything; it's only responsible for
initializing the instance after it's been created.
In general, you shouldn't need to override __new__
unless you're
subclassing an immutable type like str, int, unicode or tuple.
The *args
is used in the __new__
signature to allow an arbitrary number of arguments to be passed in. Using *args
again on the call to str.__new__(*args)
passes these arbitrary number of arguments on to the parent's method.
By using the call to str.__new__
you get all the parent class attributes and methods.
The __new__()
method creates and returns exactly one object. It can not be used to create multiple objects.
Post back if you need more help. Good luck!!!