What's the difference between lists and tuples?

Question

What's the difference between tuples/lists and what are their advantages/disadvantages?

Klenk

The others answered below, but I'd like to point out, that, imho, python has a totally unintuitive data type names. I don't think any other language has tuples (by that name), and whats worse as a word I can't even translate it in my language. Does anyone know where "tuple" comes from ? Dutch ? – Lighting

Tuples are a basic term in mathematics, derived from latin (see wikipedia). – Applejack

pair -> triple -> quadruple -> quintuple -> sextuple -> um, what's it called, ah sod it, 7-tuple -> 8-tuple -> ... hence 'tuple' as a generic name. – Deflect

@JohnFouhy It's over six years later, but: ...heptuple, octuple, tuple-with-nine-elements, decuple, undecuple, dodecuple... :D – Godin

@Godin It's over two years later, but: 9-tuple = nontuple ;) – Template

@Template I thought we'd established that a nontuple was a list. ;D – Godin

@Lighting Swift has tuples. – Isomerism

Answer 1

Apart from tuples being immutable there is also a semantic distinction that should guide their usage. Tuples are heterogeneous data structures (i.e., their entries have different meanings), while lists are homogeneous sequences. Tuples have structure, lists have order.

Using this distinction makes code more explicit and understandable.

One example would be pairs of page and line number to reference locations in a book, e.g.:

my_location = (42, 11)  # page number, line number

You can then use this as a key in a dictionary to store notes on locations. A list on the other hand could be used to store multiple locations. Naturally one might want to add or remove locations from the list, so it makes sense that lists are mutable. On the other hand it doesn't make sense to add or remove items from an existing location - hence tuples are immutable.

There might be situations where you want to change items within an existing location tuple, for example when iterating through the lines of a page. But tuple immutability forces you to create a new location tuple for each new value. This seems inconvenient on the face of it, but using immutable data like this is a cornerstone of value types and functional programming techniques, which can have substantial advantages.

There are some interesting articles on this issue, e.g. "Python Tuples are Not Just Constant Lists" or "Understanding tuples vs. lists in Python". The official Python documentation also mentions this

"Tuples are immutable, and usually contain an heterogeneous sequence ...".

In a statically typed language like Haskell the values in a tuple generally have different types and the length of the tuple must be fixed. In a list the values all have the same type and the length is not fixed. So the difference is very obvious.

Finally there is the namedtuple in Python, which makes sense because a tuple is already supposed to have structure. This underlines the idea that tuples are a light-weight alternative to classes and instances.

Applejack

"lists are homogeneous sequences" - I'm new to Python, but aren't lists heterogeneous? From docs.python.org/py3k/tutorial/introduction.html : "List items need not all have the same type." But maybe you're speaking about the formal concept, and not the Python take on it. – Casares

1. Heterogenous lists are OK - what's usually needed is some homogenous interface among the elements. 2. Using a tuple in place of an immutable list is a form of micro-optimisation. – Octaviooctavius

A good semantic synonym for "tuple" might be "record." It's a collection of related data items in a specific sequence. In fact I feel like collections.namedtuple would be better called collections.record. It would make no sense to swap, say, the name and address in a customer record; in fact, doing so would generally be an error, which the tuple's immutability prevents you from committing. – Diagraph

In fact I just remembered that the ancient DIF file format uses the term "tuple" to refer to a row, or record, of data. – Diagraph

So I just read the James Tauber blog post, and immediately thought "ok, then what's the difference between namedtuple and a dictionary?" Just immutability, I suppose, since there's no longer any real semantic difference.... – Hock

You could probably still use a list everywhere where tuples are used without major problems. So one could see tuples as specialization of lists and that's how I think they should be seen. It's not really about structure or order. Tuples are just immutable lists of length two. – Disaster

@naught101: No, not really. Namedtuples are more like light-weight classes, they don't have much in common with dicts. – Applejack

@Triliarion: Of course you can ignore the semantic distinction without causing any direct technical problem. But I think my answer provides good reasons why you should not do that. – Applejack

The "just" part of "tuples are not just immutable lists" is important, because, along with being usable as static-shaped heterogeneous records, they're also usable as homogenous sequences that are just like lists except immutable—so, e.g., you can use them as a set element or dict key (or as a multi-dimensional array index, for that matter). Your answer is completely right that usually you use a tuple because you want a light-weight record, it's just that "usually" isn't "always". – Luxemburg

@naught101: The main difference between a namedtuple and a dictionary is that the namedtuple has attributes, with static names that are part of the source code, while a dictionary has members, with dynamic names that are part of your data. (Of course you can fudge this difference by using getattr with data/indexing with literals, and occasionally you have to, but usually you don't want to.) – Luxemburg

@abarnert: True, that is an important point (and I'm not arguing against this). To some extend this fits the semantic distinction, because there are probably more situations where you would use structured tuples as dict keys or set values than lists (e.g., using a book location as a dict key makes sense, using a list of locations as a key is less common). But of course there are legitimate counterexamples (e.g., polynomials encoded in the standard way like [3,0,0,1]). – Applejack

@nikow: Thanks for coming up with a good example for my point. :) Anyway, I agree with you that there are probably more situations where you want a set of structured tuples than sequences, I just wanted to point out that it's not 100%, because it's the only minor issue your answer doesn't already cover perfectly. – Luxemburg

@nikow: Regarding What would you do with such a list?, I always shiver when ppl use lack of fantasy as an argument. Using mixed type lists works great e.g. for some hierarchical data structures, where each list is composed of child-lists and value-elements. – Shrewsbury

@phresnel: In your hierarchical data structure example I would not consider the list to be heterogenous. In the standard composite pattern both leaves and composites are subclasses of a component base class - so you have a homogenous list of components and use polymorphism. – Applejack

@nikow: Except when using polymorphism makes the code less readable. In the general case, I agree. But in small, very local pieces of code, a list of (element, list) is often worth a thousand classes. – Shrewsbury

@phresnel: You realize that what you just wrote is a tuple, not a list, and therefore you're actually making nikow's point here? (That's not to say that you can't come up with examples where using a list as a mutable tuple makes sense, just like the examples I gave of using a tuple as an immutable list so you can stick it in a set, just that there are default intended semantics; that's why the first thing you think of when you want a heterogenous pair is a tuple. – Luxemburg

Isn't it misleading to say tuples are heterogeneous and lists are homogeneous? For example a list can have mixtures of different data types i.e. l = [1, 2, 'a']. I don't understand what you're talking about. – Pyrogen

Drawing a parallel to a language like 'C' would it be correct to say that tuples are similar to structs whereas lists are similar to arrays? – Flange

@Akshay: Yes, exactly (especially namedtuples). – Applejack

@Pyrogen It is misleading in a strict sense because the language does not enforce homogeneity in lists (Python is for consenting adults, after all). The point is more about writing code within the conventions of the community. In such a context, the tuples and lists have different semantic meanings that can clarify what the code is meant to do. – Soybean

The key here is that 'heterogeneous" and "homogeneous" in this post are referring to semantic kind not programmatic type. This is quite natural in a object-oriented context using IsA inheritance, but it also make sense in @Sebastian's tree example as long as we understand that the list contents are subtrees which may be (implicitly) empty, leafs, or branches. (The tree case is also exactly how lisp is structured.) – Precondition

I think that apart from the "heterogeneous" vs. "homogeneous" distinction there is also an ordering distinction. In the location example given above, both elements are of the same type - integer - but their ordering matters. Reversing the coordinates gives a different location. Although sometimes a list has a particular order, and often we want to know what is the head or the tail, in many cases reordering a list makes no semantic difference. – Introduction

Answer 2

Difference between list and tuple

1. Literal

   someTuple = (1,2)
   someList  = [1,2] 
   

2. Size

   a = tuple(range(1000))
   b = list(range(1000))
   
   a.__sizeof__() # 8024
   b.__sizeof__() # 9088
   

   Due to the smaller size of a tuple operation, it becomes a bit faster, but not that much to mention about until you have a huge number of elements.

3. Permitted operations

   b    = [1,2]   
   b[0] = 3       # [3, 2]
   
   a    = (1,2)
   a[0] = 3       # Error
   

   That also means that you can't delete an element or sort a tuple. However, you could add a new element to both list and tuple with the only difference that since the tuple is immutable, you are not really adding an element but you are creating a new tuple, so the id of will change

   a     = (1,2)
   b     = [1,2]  
   
   id(a)          # 140230916716520
   id(b)          # 748527696
   
   a   += (3,)    # (1, 2, 3)
   b   += [3]     # [1, 2, 3]
   
   id(a)          # 140230916878160
   id(b)          # 748527696
   

4. Usage

   As a list is mutable, it can't be used as a key in a dictionary, whereas a tuple can be used.

   a    = (1,2)
   b    = [1,2] 
   
   c = {a: 1}     # OK
   c = {b: 1}     # Error
   

Deprived

So what happens when I try to resize the list size to large values? Will it change the memory address (which I believe should change the id). Or will it throw me an error? – Doralynne

@WanderingMind: the memory address where the list values are stored is not the same as the memory address where the list object itself is stored. – Kellner

Why isn't sorting permitted on a tuple? Is it because it contains heterogeneous items? – Flashover

Hmmm ... all the code in this post except the first box under 3. Permitted operation shows the tuple case first. I know it is usual to show success then error, but that messed with my head for a few moments. – Precondition

As shown under point 3, a single element list can be one_item_list = [a], but one_tuple = (a,) is the corresponding tuple. Note the comma following the variable name. But also note two_tuple = (a, b). This threw me off more than once (still there in Python 3). – Bonny

@Flashover Because sorting the tuple would mutate it, i.e., change its items. Tuples don't support that. The simplest way to obtain a sorted tuple in python is tuple(sorted(the_unsorted_tuple)) – Brushwork

Answer 3

If you went for a walk, you could note your coordinates at any instant in an (x,y) tuple.

If you wanted to record your journey, you could append your location every few seconds to a list.

But you couldn't do it the other way around.

Hetman

This example looks like merely a convention. People could argue "I can still use [x, y] to note coordinates if I want". Therefore, this answer is considered uncompleted unless one more sentence: "Read @Applejack 's post for why you should not use list to store coordinates" – Goldeye

@Iceberg, my answer is meant to help develop intuition. It's not meant to explore every nuance of the topic. – Hetman

Nice example +1. It emphasizes the complementary nature of the tuple elements (here the coordinates), which is the reason why modifying any one of them is not allowed -- because it changes the meaning of the whole tuple (here the position of one point). – Aurel

Answer 4

The key difference is that tuples are immutable. This means that you cannot change the values in a tuple once you have created it.

So if you're going to need to change the values use a List.

Benefits to tuples:

1. Slight performance improvement.
2. As a tuple is immutable it can be used as a key in a dictionary.
3. If you can't change it neither can anyone else, which is to say you don't need to worry about any API functions etc. changing your tuple without being asked.

Kinshasa

Note that a tuple is only immutable if all of its elements are. You could say the same is true of all immutable collections, like frozenset or the various third-party frozen dict/tree/etc. types, but none of those allow you to add mutable elements. (And of course a tuple is only hashable if all of its elements are, which is handles in the usual EAFP way, so d[1, [2]] will raise TypeError: unhashable type: 'list'.) – Luxemburg

A tuple can only be used as a key in a dictionary if all of its elements are immutable. See here – Rattletrap

Answer 5

Lists are mutable; tuples are not.

From docs.python.org/2/tutorial/datastructures.html

Tuples are immutable, and usually contain an heterogeneous sequence of elements that are accessed via unpacking (see later in this section) or indexing (or even by attribute in the case of namedtuples). Lists are mutable, and their elements are usually homogeneous and are accessed by iterating over the list.

Brachiopod

I really think you should also consider the semantic implications (see my answer below). – Applejack

Hardly seems worth the effort now, but thanks for the heads up. – Brachiopod

OK, here's the link - docs.python.org/2/library/stdtypes.html#mutable-sequence-types ;-) – Nombles

@Brachiopod I think this answer is the clearest and most concise on this page. It names the sole really important difference between tuples and lists and doesn't babble on endlessly about this blatantly false homogeneous-vs-heterogeneous hogwash. – Spraddle

Answer 6

This is an example of Python lists:

my_list = [0,1,2,3,4]
top_rock_list = ["Bohemian Rhapsody","Kashmir","Sweet Emotion", "Fortunate Son"]

This is an example of Python tuple:

my_tuple = (a,b,c,d,e)
celebrity_tuple = ("John", "Wayne", 90210, "Actor", "Male", "Dead")

Python lists and tuples are similar in that they both are ordered collections of values. Besides the shallow difference that lists are created using brackets "[ ... , ... ]" and tuples using parentheses "( ... , ... )", the core technical "hard coded in Python syntax" difference between them is that the elements of a particular tuple are immutable whereas lists are mutable (...so only tuples are hashable and can be used as dictionary/hash keys!). This gives rise to differences in how they can or can't be used (enforced a priori by syntax) and differences in how people choose to use them (encouraged as 'best practices,' a posteriori, this is what smart programers do). The main difference a posteriori in differentiating when tuples are used versus when lists are used lies in what meaning people give to the order of elements.

For tuples, 'order' signifies nothing more than just a specific 'structure' for holding information. What values are found in the first field can easily be switched into the second field as each provides values across two different dimensions or scales. They provide answers to different types of questions and are typically of the form: for a given object/subject, what are its attributes? The object/subject stays constant, the attributes differ.

For lists, 'order' signifies a sequence or a directionality. The second element MUST come after the first element because it's positioned in the 2nd place based on a particular and common scale or dimension. The elements are taken as a whole and mostly provide answers to a single question typically of the form, for a given attribute, how do these objects/subjects compare? The attribute stays constant, the object/subject differs.

There are countless examples of people in popular culture and programmers who don't conform to these differences and there are countless people who might use a salad fork for their main course. At the end of the day, it's fine and both can usually get the job done.

To summarize some of the finer details

Similarities:

1. Duplicates - Both tuples and lists allow for duplicates

2. Indexing, Selecting, & Slicing - Both tuples and lists index using integer values found within brackets. So, if you want the first 3 values of a given list or tuple, the syntax would be the same:

   >>> my_list[0:3]
   [0,1,2]
   >>> my_tuple[0:3]
   [a,b,c]
   

3. Comparing & Sorting - Two tuples or two lists are both compared by their first element, and if there is a tie, then by the second element, and so on. No further attention is paid to subsequent elements after earlier elements show a difference.

   >>> [0,2,0,0,0,0]>[0,0,0,0,0,500]
   True
   >>> (0,2,0,0,0,0)>(0,0,0,0,0,500)
   True
   

Differences: - A priori, by definition

1. Syntax - Lists use [], tuples use ()

2. Mutability - Elements in a given list are mutable, elements in a given tuple are NOT mutable.

   # Lists are mutable:
   >>> top_rock_list
   ['Bohemian Rhapsody', 'Kashmir', 'Sweet Emotion', 'Fortunate Son']
   >>> top_rock_list[1]
   'Kashmir'
   >>> top_rock_list[1] = "Stairway to Heaven"
   >>> top_rock_list
   ['Bohemian Rhapsody', 'Stairway to Heaven', 'Sweet Emotion', 'Fortunate Son']
   
   # Tuples are NOT mutable:       
   >>> celebrity_tuple
   ('John', 'Wayne', 90210, 'Actor', 'Male', 'Dead')
   >>> celebrity_tuple[5]
   'Dead'
   >>> celebrity_tuple[5]="Alive"
   Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   TypeError: 'tuple' object does not support item assignment
   

3. Hashtables (Dictionaries) - As hashtables (dictionaries) require that its keys are hashable and therefore immutable, only tuples can act as dictionary keys, not lists.

   #Lists CAN'T act as keys for hashtables(dictionaries)
   >>> my_dict = {[a,b,c]:"some value"}
   Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   TypeError: unhashable type: 'list'
   
   #Tuples CAN act as keys for hashtables(dictionaries)
   >>> my_dict = {("John","Wayne"): 90210}
   >>> my_dict
   {('John', 'Wayne'): 90210}
   

Differences - A posteriori, in usage

1. Homo vs. Heterogeneity of Elements - Generally list objects are homogenous and tuple objects are heterogeneous. That is, lists are used for objects/subjects of the same type (like all presidential candidates, or all songs, or all runners) whereas although it's not forced by), whereas tuples are more for heterogenous objects.

2. Looping vs. Structures - Although both allow for looping (for x in my_list...), it only really makes sense to do it for a list. Tuples are more appropriate for structuring and presenting information (%s %s residing in %s is an %s and presently %s % ("John","Wayne",90210, "Actor","Dead"))

Attest

I like the hashtable/hashable example for explaining a reason for immutability-- you can use a tuple(record/struct/coordinate/vector/point) as a complex key into a dict. – Parotitis

Answer 7

It's been mentioned that the difference is largely semantic: people expect a tuple and list to represent different information. But this goes further than a guideline; some libraries actually behave differently based on what they are passed. Take NumPy for example (copied from another post where I ask for more examples):

>>> import numpy as np
>>> a = np.arange(9).reshape(3,3)
>>> a
array([[0, 1, 2],
       [3, 4, 5],
       [6, 7, 8]])
>>> idx = (1,1)
>>> a[idx]
4
>>> idx = [1,1]
>>> a[idx]
array([[3, 4, 5],
       [3, 4, 5]])

The point is, while NumPy may not be part of the standard library, it's a major Python library, and within NumPy lists and tuples are completely different things.

Bathhouse

This isn't really a helpful answer. The difference is that type(a_list) != type(a_tuple), so any piece of library code branching based on type(x) will behave differently – Ilium

good point, I've edited the post: this is really just pointing out that the semantic guidelines are hardcoded into some libraries. – Bathhouse

It might be better to use examples from the stdlib/builtins than from third-party libraries. There are a number of places where you can use a single value or a tuple of values, and a list or other sequence is considered a single value. For example, '%d %d' % [2, 3] is a TypeError, because you're trying to pass a list to the first %d and you're not passing any value to the second %d. (However, there are counter-examples to this too, like max…) – Luxemburg

that's interesting, I didn't know there were any examples of this in the python standard library. A number of places you say? – Bathhouse

The value you'll get from this answer largely depends on the type of python programming you do. If you're doing scientific/statistical programming, you'll likely find the numpy example quite salient. This is also a common interview question so numpy is a pretty useful example to have in your pocket. – Cully

Answer 8

Lists are for looping, tuples are for structures i.e. "%s %s" %tuple.

Lists are usually homogeneous, tuples are usually heterogeneous.

Lists are for variable length, tuples are for fixed length.

Recrudesce

Answer 9

The values of list can be changed any time but the values of tuples can't be change.

The advantages and disadvantages depends upon the use. If you have such a data which you never want to change then you should have to use tuple, otherwise list is the best option.

Infinite

Answer 10

Difference between list and tuple

Tuples and lists are both seemingly similar sequence types in Python.

1. Literal syntax

   We use parenthesis () to construct tuples and square brackets [ ] to get a new list. Also, we can use call of the appropriate type to get required structure — tuple or list.

   someTuple = (4,6)
   someList  = [2,6] 
   

2. Mutability

   Tuples are immutable, while lists are mutable. This point is the base the for the following ones.

3. Memory usage

   Due to mutability, you need more memory for lists and less memory for tuples.

4. Extending

   You can add a new element to both tuples and lists with the only difference that the id of the tuple will be changed (i.e., we’ll have a new object).

5. Hashing

   Tuples are hashable and lists are not. It means that you can use a tuple as a key in a dictionary. The list can't be used as a key in a dictionary, whereas a tuple can be used

   tup      = (1,2)
   list_    = [1,2] 
   
   c = {tup   : 1}     # ok
   c = {list_ : 1}     # error
   

6. Semantics

   This point is more about best practice. You should use tuples as heterogeneous data structures, while lists are homogenous sequences.

Wines

This is a good answer, especially pointing out the reason for the memory difference between both data structures. – Gallaher

Answer 11

Lists are intended to be homogeneous sequences, while tuples are heterogeneous data structures.

Bahr

At this point, this answer doesn't add anything to the discussion, as there are many other better answers. – Valerie

Answer 12

The PEP 484 -- Type Hints says that the types of elements of a tuple can be individually typed; so that you can say Tuple[str, int, float]; but a list, with List typing class can take only one type parameter: List[str], which hints that the difference of the 2 really is that the former is heterogeneous, whereas the latter intrinsically homogeneous.

Also, the standard library mostly uses the tuple as a return value from such standard functions where the C would return a struct.

Castano

Answer 13

As people have already answered here that tuples are immutable while lists are mutable, but there is one important aspect of using tuples which we must remember

If the tuple contains a list or a dictionary inside it, those can be changed even if the tuple itself is immutable.

For example, let's assume we have a tuple which contains a list and a dictionary as

my_tuple = (10,20,30,[40,50],{ 'a' : 10})

we can change the contents of the list as

my_tuple[3][0] = 400
my_tuple[3][1] = 500

which makes new tuple looks like

(10, 20, 30, [400, 500], {'a': 10})

we can also change the dictionary inside tuple as

my_tuple[4]['a'] = 500

which will make the overall tuple looks like

(10, 20, 30, [400, 500], {'a': 500})

This happens because list and dictionary are the objects and these objects are not changing, but the contents its pointing to.

So the tuple remains immutable without any exception

Leahleahey

This post would be improved if you explained that "those can be changed even if the tuple itself in immutable." is because those object retain their identity while (so the tuple hasn't changed because it still contains the same objects...). – Precondition

Answer 14

As people have already mentioned the differences I will write about why tuples.

Why tuples are preferred?

Allocation optimization for small tuples

To reduce memory fragmentation and speed up allocations, Python reuses old tuples. If a tuple no longer needed and has less than 20 items instead of deleting it permanently Python moves it to a free list.

A free list is divided into 20 groups, where each group represents a list of tuples of length n between 0 and 20. Each group can store up to 2 000 tuples. The first (zero) group contains only 1 element and represents an empty tuple.

>>> a = (1,2,3)
>>> id(a)
4427578104
>>> del a
>>> b = (1,2,4)
>>> id(b)
4427578104

In the example above we can see that a and b have the same id. That is because we immediately occupied a destroyed tuple which was on the free list.

Allocation optimization for lists

Since lists can be modified, Python does not use the same optimization as in tuples. However, Python lists also have a free list, but it is used only for empty objects. If an empty list is deleted or collected by GC, it can be reused later.

>>> a = []
>>> id(a)
4465566792
>>> del a
>>> b = []
>>> id(b)
4465566792

Source: https://rushter.com/blog/python-lists-and-tuples/

Why tuples are efficient than lists? -> https://stackoverflow.com/a/22140115

Underskirt

Answer 15

The most important difference is time ! When you do not want to change the data inside the list better to use tuple ! Here is the example why use tuple !

import timeit
print(timeit.timeit(stmt='[1,2,3,4,5,6,7,8,9,10]', number=1000000)) #created list
print(timeit.timeit(stmt='(1,2,3,4,5,6,7,8,9,10)', number=1000000)) # created tuple 

In this example we executed both statements 1 million times

Output :

0.136621
0.013722200000000018

Any one can clearly notice the time difference.

Ruddock

But why is it faster? – Puzzle

@HarryMoreno Technically, tuples are faster because they are immutable. – Gallaher

Answer 16

A direction quotation from the documentation on 5.3. Tuples and Sequences:

Though tuples may seem similar to lists, they are often used in different situations and for different purposes. Tuples are immutable, and usually contain a heterogeneous sequence of elements that are accessed via unpacking (see later in this section) or indexing (or even by attribute in the case of namedtuples). Lists are mutable, and their elements are usually homogeneous and are accessed by iterating over the list.

Biogeochemistry

Answer 17

Just a quick extension to list vs tuple responses:

• Due to dynamic nature, list allocates more bit buckets than the actual memory required. This is done to prevent costly reallocation operation in case extra items are appended in the future.

• On the other hand, being static, lightweight tuple object does not reserve extra memory required to store them.

Thurston

Are these bit buckets just extra "space" for future items? And how does it determine the size and number of the buckets? – Arlinearlington

Answer 18

First of all, they both are the non-scalar objects (also known as a compound objects) in Python.

• Tuples, ordered sequence of elements (which can contain any object with no aliasing issue)
  • Immutable (tuple, int, float, str)
  • Concatenation using + (brand new tuple will be created of course)
  • Indexing
  • Slicing
  • Singleton (3,) # -> (3) instead of (3) # -> 3
• List (Array in other languages), ordered sequence of values
  • Mutable
  • Singleton [3]
  • Cloning new_array = origin_array[:]
  • List comprehension [x**2 for x in range(1,7)] gives you [1,4,9,16,25,36] (Not readable)

Using list may also cause an aliasing bug (two distinct paths pointing to the same object).

Dogcatcher

Answer 19

Lists are mutable and tuples are immutable. Just consider this example.

a = ["1", "2", "ra", "sa"]    #list
b = ("1", "2", "ra", "sa")    #tuple

Now change index values of list and tuple.

a[2] = 1000
print a     #output : ['1', '2', 1000, 'sa']
b[2] = 1000
print b     #output : TypeError: 'tuple' object does not support item assignment.

Hence proved the following code is invalid with tuple, because we attempted to update a tuple, which is not allowed.

Rhaetian

Answer 20

Lists are mutable. whereas tuples are immutable. Accessing an offset element with index makes more sense in tuples than lists, Because the elements and their index cannot be changed.

Irk

Answer 21

In other words, TUPLES are used to store group of elements where the contents/members of the group would not change while LISTS are used to store group of elements where the members of the group can change.

For instance, if i want to store IP of my network in a variable, it's best i used a tuple since the the IP is fixed. Like this my_ip = ('192.168.0.15', 33, 60). However, if I want to store group of IPs of places I would visit in the next 6 month, then I should use a LIST, since I will keep updating and adding new IP to the group. Like this

places_to_visit = [
    ('192.168.0.15', 33, 60), 
    ('192.168.0.22', 34, 60), 
    ('192.168.0.1', 34, 60), 
    ('192.168.0.2', 34, 60), 
    ('192.168.0.8', 34, 60), 
    ('192.168.0.11', 34, 60)
] 

Undernourished

Answer 22

List is mutable and tuples is immutable. The main difference between mutable and immutable is memory usage when you are trying to append an item.

When you create a variable, some fixed memory is assigned to the variable. If it is a list, more memory is assigned than actually used. E.g. if current memory assignment is 100 bytes, when you want to append the 101th byte, maybe another 100 bytes will be assigned (in total 200 bytes in this case).

However, if you know that you are not frequently add new elements, then you should use tuples. Tuples assigns exactly size of the memory needed, and hence saves memory, especially when you use large blocks of memory.

Varien

While some of that is technically true, that isn't really the crucial difference between mutable and immutable types. The bigger difference is that mutable types can be changed after construction, while immutable types can't. – Ophir

That's not the why either. Memory and mutability have nothing to do with each other. That's simply an implementation detail specific to lists. Memory is also not assigned to variables, it's assigned to the objects. Variables are then just references to those objects. – Ophir