def test(nums):
nums = list(set(nums))
nums = [1,2,3,4,1,2,3,4]
test(nums)
print(nums)
[1,2,3,4,1,2,3,4]
I am not able to understand the process. If I do something like
def test(nums):
nums.append(7)
nums = [1,2,3,4,1,2,3,4]
test(nums)
print(nums)
[1,2,3,4,1,2,3,4,7]
the list alters.
everything is object in python
when you are using object method inside any function then python changes that object depending upon that method. append is inplace in your case
In this case,
def test(nums):
nums.append(7)
nums = [1,2,3,4,1,2,3,4]
test(nums)
print(nums)
nums is list object, and you are calling append method on that list object which is inplace so it is changing the original list.
While in this case,
def test(nums):
nums = list(set(nums))
nums = [1,2,3,4,1,2,3,4]
test(nums)
print(nums)
you have passed your list object to your function, but nums = list(set(nums)) in this line, you assigned a new list object to nums and previous nums is lost.
for clarification you can print the id of these objects,
def test(nums):
print(id(nums)) # this will be original list id
nums = list(set(nums))
print(id(nums)) # this will be changed
nums = [1,2,3,4,1,2,3,4]
print(id(nums)) # this will be original list id
test(nums)
print(id(nums)) # this will be original list id
print(nums)
and for other case,
def test(nums):
print(id(nums)) # this will be original list id
nums.append(7)
print(id(nums)) # this will be original list id
nums = [1,2,3,4,1,2,3,4]
print(id(nums)) # this will be original list id
test(nums)
print(id(nums)) # this will be original list id
print(nums)
If you do
def test(nums):
print(id(nums)) # this will be original list id
nums[:] = [1,2,3]
print(id(nums)) # this will be original list id
nums = [1,2,3,4,1,2,3,4]
print(id(nums)) # this will be original list id
test(nums)
print(id(nums)) # this will be original list id
print(nums)
In this case, also when you do slicing then __getitem__ and __setitem__ dunder methods are used, which change the list object inplace.
