How to allow list append() method to return the new list

Question

I want to do something like this:

myList = [10,20,30]
yourList = myList.append (40)

Unfortunately, list append does not return the modified

Answer 1

You only need to do myList.append(40)

It will append it to the original list, not return a new list.

Answer 2

Don't use append but concatenation instead:

yourList = myList + [40]

This returns a new list; myList will not be affected. If you need to have myList affected as well either use .append() anyway, then assign yourList separately from (a copy of) myList.

Answer 3

Just to expand on Storstamp's answer

You only need to do myList.append(40)

It will append it to the original list,now you can return the variable containing the original list.

If you are working with very large lists this is the way to go.

Answer 4

Try using itertools.chain(myList, [40]). That will return a generator as a sequence, rather than allocating a new list. Essentially, that returns all of the elements from the first iterable until it is exhausted, then proceeds to the next iterable, until all of the iterables are exhausted.

Answer 5

list.append is a built-in and therefore cannot be changed. But if you're willing to use something other than append, you could try +:

In [106]: myList = [10,20,30]

In [107]: yourList = myList + [40]

In [108]: print myList
[10, 20, 30]

In [109]: print yourList
[10, 20, 30, 40]

Of course, the downside to this is that a new list is created which takes a lot more time than append

Hope this helps

Answer 6

You can subclass the built-in list type and redefine the 'append' method. Or even better, create a new one which will do what you want it to do. Below is the code for a redefined 'append' method.

#!/usr/bin/env python

class MyList(list):

  def append(self, element):
    return MyList(self + [element])


def main():
  l = MyList()
  l1 = l.append(1)
  l2 = l1.append(2)
  l3 = l2.append(3)
  print "Original list: %s, type %s" % (l, l.__class__.__name__)
  print "List 1: %s, type %s" % (l1, l1.__class__.__name__)
  print "List 2: %s, type %s" % (l2, l2.__class__.__name__)
  print "List 3: %s, type %s" % (l3, l3.__class__.__name__)


if __name__ == '__main__':
  main()

Hope that helps.