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

[1,2,3] is a list.

(1,2,3) is a tuple and immutable.

Answer 2

From the Python FAQ:

Lists and tuples, while similar in many respects, are generally used in fundamentally different ways. Tuples can be thought of as being similar to Pascal records or C structs; they're small collections of related data which may be of different types which are operated on as a group. For example, a Cartesian coordinate is appropriately represented as a tuple of two or three numbers.

Lists, on the other hand, are more like arrays in other languages. They tend to hold a varying number of objects all of which have the same type and which are operated on one-by-one.

Generally by convention you wouldn't choose a list or a tuple just based on its (im)mutability. You would choose a tuple for small collections of completely different pieces of data in which a full-blown class would be too heavyweight, and a list for collections of any reasonable size where you have a homogeneous set of data.

Answer 3

In simple words, lists are mutable whereas tuples are not. Hence, if you want to modify the elements in your program i.e., adding, deleting or altering elements, go for a list. But, if you don't want tat to happen i.e., may be for setting sequence in for loop, etc. go for a tuple

Answer 4

(1,2,3) is a tuple and [1,2,3] is a list. You either of the two represent sequences of numbers but note that tuples are immutable and list are mutable Python objects.

Answer 5

The notion of tuples are highly expressive:

• Pragmatically, they are great for packing and unpacking values (x,y=coord).

• In combination with dictionaries (hash tables), they allow forms of mapping that would otherwise require many levels of association. For example, consider marking that (x,y) has been found.

  // PHP
  if (!isset($found[$x])) {
      $found[$x] = Array();
      $found[$x][$y] = true;
  } else if (!isset($found[$x][$y])) {
      $found[$x][$y] = true;
  }
  
  # Python
  found[(x,y)] = True # parens added for clarity
  

• Lists should be used with the expectation of operations on its contents (hence the various mentions of immutability). One will want to pop, push, splice, slice, search, insert before, insert after, etc with a list.

• Tuples should be a low-level representation of an object, where simple comparisons are made, or operations such as extracting the n'th element or n elements in a predictable fashion, such as the coordinates example given earlier.

• Lastly, lists are not hashable, so the type of mapping done with dictionaries (hash tables in Perl, associative arrays in PHP) must be done with tuples.

  Here's a simple example of tuples and dictionaries, together at last:

  """
  couple is a tuple of two people
  doesLike is a dictionary mapping couples to True or False
  """
  couple = "john", "jane"
  doesLike = dict()
  doesLike[couple] = True
  doesLike["jane", "john"] = False # unrequited love :'(
  

Answer 6

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.