I have this function to simulate reverse() in python:
My_list = [[1, 3, "s"], 2, 2, 3, 4, 2]
def listRev(list):
list=list[::-1]
print list
listRev(My_list)
print My_list
The function gives me correct reversed list but I expect when I print My_list in the last line, the code print reversed My_list not My_list itself. How can I solve my problem?
If you want to simulate reverse, you must modify the list passed as a parameter to you function, not simply use a new list in your function.
When you write list=list[::-1] the local copy of the original parameter points to a new list. You should do instead :
def rev(l):
l[:] = l[::-1]
print (l)
The usage of l[:] asks Python to replace the content of the list, and not to make the variable point to a new list.
def my_list_reverse(L): length = len(L) for i in range(length/2): L[i], L[length-i-1] = L[length-i-1], L[i]This can be solved by returning a list from the function
My_list = [[1, 3, "s"], 2, 2, 3, 4, 2]
def listRev(list):
list=list[::-1]
print list
return list
My_list = listRev(My_list)
print My_list
This is because lists are not passed by reference in Python.
Post Comment Edit
If you want the function to be in place only for My_list even though it is very wrong and bad programming to do so, you can use this
My_list = [[1, 3, "s"], 2, 2, 3, 4, 2]
def listRev():
global My_list
My_list = My_list[::-1]
listRev()
print My_list
My_list = listRev(My_list) then you will not be calling that function. Thus my_list will be My_list itself and will not be reversed.My_list as global. and change it there itself.
listas a veriable name is a bad idea.