What s the difference between lists and tuples

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What s the difference   What are the advantages   disadvantages of tuples   lists

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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

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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

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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

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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

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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

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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    Slight performance improvement  As a tuple is immutable it can be used as a key in a dictionary  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

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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

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Difference between list and tuple   Literal  someTuple    1 2  someList     1 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  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  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

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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

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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     gt  gt  gt  a    1 2 3   gt  gt  gt  id a  4427578104  gt  gt  gt  del a  gt  gt  gt  b    1 2 4   gt  gt  gt  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     gt  gt  gt  a       gt  gt  gt  id a  4465566792  gt  gt  gt  del a  gt  gt  gt  b       gt  gt  gt  id b  4465566792   Source  https   rushter com blog python-lists-and-tuples   Why tuples are efficient than lists  -  https   stackoverflow com a 22140115

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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    Duplicates - Both tuples and lists allow for duplicates Indexing  Selecting   amp  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    gt  gt  gt  my list 0 3   0 1 2   gt  gt  gt  my tuple 0 3   a b c   Comparing  amp  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    gt  gt  gt   0 2 0 0 0 0  gt  0 0 0 0 0 500  True  gt  gt  gt   0 2 0 0 0 0  gt  0 0 0 0 0 500  True    Differences  - A priori  by definition   Syntax - Lists use     tuples use    Mutability - Elements in a given list are mutable  elements in a given tuple are NOT mutable      Lists are mutable   gt  gt  gt  top rock list   Bohemian Rhapsody    Kashmir    Sweet Emotion    Fortunate Son    gt  gt  gt  top rock list 1   Kashmir   gt  gt  gt  top rock list 1     Stairway to Heaven   gt  gt  gt  top rock list   Bohemian Rhapsody    Stairway to Heaven    Sweet Emotion    Fortunate Son      Tuples are NOT mutable          gt  gt  gt  celebrity tuple   John    Wayne   90210   Actor    Male    Dead    gt  gt  gt  celebrity tuple 5   Dead   gt  gt  gt  celebrity tuple 5   Alive  Traceback  most recent call last   File   lt stdin gt    line 1  in  lt module gt  TypeError   tuple  object does not support item assignment  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   gt  gt  gt  my dict     a b c   some value   Traceback  most recent call last   File   lt stdin gt    line 1  in  lt module gt  TypeError  unhashable type   list    Tuples CAN act as keys for hashtables dictionaries   gt  gt  gt  my dict      John   Wayne    90210   gt  gt  gt  my dict    John    Wayne    90210     Differences - A posteriori  in usage   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  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

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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

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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

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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

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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     gt  gt  gt  import numpy as np  gt  gt  gt  a   np arange 9  reshape 3 3   gt  gt  gt  a array   0  1  2           3  4  5           6  7  8     gt  gt  gt  idx    1 1   gt  gt  gt  a idx  4  gt  gt  gt  idx    1 1   gt  gt  gt  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

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

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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

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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     - gt   3  instead of  3    - gt  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

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Difference between list and tuple  Tuples and lists are both seemingly similar sequence types in Python    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    Mutability   Tuples are immutable  while lists are mutable  This point is the base the for the following ones   Memory usage   Due to mutability  you need more memory for lists and less memory for tuples  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   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  Semantics   This point is more about best practice  You should use tuples as heterogeneous data structures  while lists are homogenous sequences

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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

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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

[python] What's the difference between lists and tuples?

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