If I do something like this:
a = [[0]*5]*5
print(a)
a[0][0] = 1
print(a)
Why does it change every first element in each sublist (?), and not only the first element in the first sublist?
#🔒 2D list
north hull
proud phoenixBOT
If I do something like this:
```py
a = [[0]*5]*5
print(a)
a[0][0] = 1
print(a)
`...
@north hull
Python help channel opened
north hull
!e
a = [[0]*5]*5
print(a)
a[0][0] = 1
print(a)
:white_check_mark: Your 3.12 eval job has completed with return code 0.
001 | [[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
002 | [[1, 0, 0, 0, 0], [1, 0, 0, 0, 0], [1, 0, 0, 0, 0], [1, 0, 0, 0, 0], [1, 0, 0, 0, 0]]
north hull
Oh, ok
so
a = [0]*5 # makes a deep copy and
b = [[0]*5]*5 # makes a shallow copy of the inner list?
cursive cloud
yeah it's essentially b = [a] * 5
north hull
And is there an easy way to change that?
pale flint
so
```py
a = [0]*5 # makes a deep copy and
b = [[0]*5]*5 # makes a shallow co...
you can't make a deepcopy without copy.deepcopy
every copy is a shallow copy, it just depends on if the data is mutable or not
spark cobalt
First isn't a deep copy, it's just int is immutable.
pale flint
instead of doing list multiplication, you can list comprehension instead
!e
a = [[0]*5 for _ in range(5)]
print(a)
a[0][0] = 1
print(a)
:white_check_mark: Your 3.12 eval job has completed with return code 0.
001 | [[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
002 | [[1, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
why is an int immutable?
pale flint
why is an int immutable?
because that's how it works
there's really no reason for an int to be mutable
lists/dicts/sets are mutable
we can change the data within without needing an assignment
north hull
instead of doing list multiplication, you can list comprehension instead
So I basically just have to add the inner lists with an for loop
pale flint
yes, that way it creates a new list each time
instead of copying an existing list 5 times
north hull
Great, thank you!
spark cobalt
why is an int immutable?
Why wouldn't it?
Any thing you do with an int is var=something+something or other calculation
When you do var= it makes a new reference
Also no methods that would be like var.add(5) and then var has a different value - all methods return a new thing.
As opposed to list where you keep the list but change the inside state of it. my_list[index]=something mutates the my_list - there's no my_list= to overwrite it
proud phoenixBOT
Python help channel closed