On 23/04/19 10:08 PM, Steven D'Aprano wrote:
On Tue, Apr 23, 2019 at 08:27:15PM +0530, Arup Rakshit wrote:
You probably want:
def __init__(self, list=None):
if list is None:
list = []
self.list = list
That is really a new thing to me. I didn't know. Why list=None in the
parameter list is different than in the body of __init__ method? Can you
elaborate this?
Try running this code and see what happens:
def make_default():
print("creating a new list")
return []
def function(arg=make_default()):
arg.append(1)
return arg
Now call:
function()
function()
function()
and see if you can work out what is happening.
Hint: how many new lists are created? when are they created?
Hello,
You are right. I didn't think on it, as it feels to me very natural as
per the experiences from other language like Ruby, JS. It works
differently there.
A similar Ruby code gives different output than Python does.
def make_default()
print("creating a new list")
return []
end
def function(arg=make_default())
arg.push(1)
return arg
end
# Now call:
p(function())
p(function())
p(function())
And on run:
ruby -v sample.rb
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-darwin16]
creating a new list[1]
creating a new list[1]
creating a new list[1]
But python gives to me:
creating a new list
[1]
[1, 1]
[1, 1, 1]
Python being an interpreted language works so differently than its other
2 siblings Ruby, JS. Surprised.
--
Thanks,
Arup Rakshit
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