Dynamically appending one list into another-CodePudding

I have following very simple implementation in python

 m = []
 l = []
 l.append('A')
 l.append('B')
 l.append('C')
 m.append(l)
 l.clear()
 print(m) --> this gives empty list.

i tried

 m = []
 l = []
 n = []
 l.append('A')
 l.append('B')
 l.append('C')
 n = l
 m.append(n)
 l.clear()
 print(m) --> this gives empty list too

But when i do not clear l, print(m) give me desired list which is ['A','B','C']. Why python clears list m when i clear list l. they are 2 separate variables?

CodePudding user response：

When you are passing a list to another list then it is taking its reference there So when you cleared that list your original list's element is also cleared Try this

m = []
l = []
l.append('A')
l.append('B')
l.append('C')
m.append(l.copy())  -> use list.copy()
l.clear()
print(m)

CodePudding user response：

both variables are reference pointing to the same object. to make a new list you need to do : n = l[:]