I am confused by the behaviour of the following code:
data = [0,1,2,3,4,5]
class test():
def __init__(self,data):
self.data=data
self.data2=data
def main(self):
del self.data2[3]
test_var = test(data)
test_var.main()
print(test_var.data)
print(test_var.data2)
what i would think should come out is this:
[0,1,2,3,4,5]
[0,1,2,4,5]
what i get is this:
[0,1,2,4,5]
[0,1,2,4,5]
Why is an element from the second list getting deleted when its not directly changed? Or does python handle attributes in such a way that this happens normally?
So how should i change the code that i get what i want?
Lists are mutable in Python and passed by reference. Whenever you assign it or pass it as an argument, a reference to it is passed and not a copy. Hence the outcome you're seeing. If you really want to mutate it, you need to deepcopy it.
import copy
class test():
def __init__(self, data):
self.data = copy.deepcopy(data)
self.data2 = copy.deepcopy(data2)
# if the list is going to be flat and just contain basic immutable types,
# slicing (or shallow-copy) would do the job just as well.
class test():
def __init__(self, data):
self.data = data[::] # or data[:] for that matter as @Joe Iddon suggested
self.data2 = data[::]
Note: not all types of objects support "deep-copying".