Can I add an operation to a list in Python?

Question

I am quite often using Python instead of pseudocode. For that, I would like to have a stack. I know that using lists is the way to go (source), but I would like to use myList.push rather than myList.append to make clear that I use a stack.

I thought I could do something simple like

myList.push = myList.append

to define an alias for the append operation, but I get

    stack.push = stack.append
AttributeError: 'list' object has no attribute 'push'

Does a short solution for adding a push-operation to a list exist?

^{(It should not mess up my runnable Python-pseudocode)}

so your question is really can you assign an alias to list.append(x) where the alias would be something like push(x) ? — Inbar Rose
– Inbar Rose, Commented Aug 7, 2012 at 7:49

Raymond Hettinger · Accepted Answer · 2012-08-07 07:29:05Z

18

You can make a subclass of list like this:

class List(list):
    def push(self, x):
        self.append(x)

Use your custom class the same way you would use a regular list:

>>> s = List()
>>> s.push(10)
>>> s.push(20)
>>> s
[10, 20]

answered Aug 7, 2012 at 7:29

Raymond Hettinger

229k67 gold badges405 silver badges504 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

monkut Over a year ago

doesn't "push" add it to the front? in which case .insert(0,x) should be used.

Dmitry Zagorulkin Over a year ago

deques will be faster than lists for this purposes.

mhawke Over a year ago

@monkut: that sounds reasonable, however, the inverse operation (list.pop) pops the last item off the list by default. So it's better to implement push with list.append so you don't have to pop(0) or override pop in the subclass.

monkut Over a year ago

good point, I wasn't thinking of pop. Probably better to use append then.

Raymond Hettinger Over a year ago

For a LIFO stack, subclass from list, make push() delegate to append() for adding values, and use pop() for removing values. For a FIFO queue, subclass from collections.deque, make push() delegate to appendleft(), and use pop() for removing values.

Vinayak Kolagi · Accepted Answer · 2012-08-07 07:56:28Z

5

Instead of redefining, how about aliasing the same function ?

class List(list):
    def __init__(self):
        self.push = self.append

This would retain the functionality of append too.

answered Aug 7, 2012 at 7:56

Vinayak Kolagi

1,8911 gold badge13 silver badges26 bronze badges

1 Comment

mhawke Over a year ago

This is OK. To preserve list construction semantics (e.g. List((1,2,3,4)) you could make the __init__ method accept *args and **kwargs and then pass these to the base class __init__ via super(List, self).__init__(*args, **kwargs)

Inbar Rose · Accepted Answer · 2012-08-07 08:28:02Z

2

>>> a = []
>>> push  = a.append
>>> push(1)
>>> a
[1]
>>>

answered Aug 7, 2012 at 8:28

Inbar Rose

43.7k24 gold badges91 silver badges137 bronze badges

1 Comment

Martin Thoma Over a year ago

Thanks for your answer. This is what I thought of but couldn't remember. Though, I accepted the other answer as I think adding 3 lines to my pseudocode is ok and the result looks a little bit cleaner => +1 for your answer

spacebat777 · Accepted Answer · 2017-04-19 04:22:38Z

1

>>> stack = type('stack', (list,), {'push':list.append})()
>>> stack.push(1)
>>> stack.pop()
1
>>>

answered Apr 19, 2017 at 4:22

spacebat777

113 bronze badges

Collectives™ on Stack Overflow

Can I add an operation to a list in Python?

4 Answers 4

5 Comments

1 Comment

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

5 Comments

1 Comment

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related