Python: what is the difference between (1,2,3) and [1,2,3], and when should I use each?

Question

In many places, (1,2,3) (a tuple) and [1,2,3] (a list) can be used interchangeably.

When should I use one or the other, and why?

Answer 1

open a console and run python. Try this:

  >>> list = [1, 2, 3]     
  >>> dir(list)
    ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__delsli
    ce__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getit
    em__', '__getslice__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__',
     '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__r
    educe__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__'
    , '__setitem__', '__setslice__', '__sizeof__', '__str__', '__subclasshook__', 
'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

As you may see the last on the last line list have the following methods: 'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort'

Now try the same for tuple:

>>> tuple = (1, 2, 3)
>>> dir(tuple)
    ['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__
    format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__get
    slice__', '__gt__', '__hash__', '__init__', '__iter__', '__le__', '__len__', '__
    lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__'
    , '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'count', 'index']

Only 'count' and 'index' from list methods appears here.

This is because tuples are immutable and they don't support any modifications. Instead they are simpler and faster in internal implementation.