How to change values in a tuple

Question

I have a tuple called values which contains the following    275    54000    0 0    5000 0    0 0    I want to change the first value  i e   275  in this tuple but I understand that tuples are immutable so values 0    200 will not work  How can I achieve this

User · Answer

tldr  the  workaround  is creating a new tuple object  not actually modifying the original  While this is a very old question  someone told me about this Python mutating tuples madness   Which I was very much surprised intrigued  and doing some googling  I landed here  and other similar samples online   I ran some test to prove my theory  Note    does value equality while is does referential equality  is obj a the same instance as obj b   a     apple    canana    cherry   b   tuple   apple    canana    cherry    c   a  print  a      str a   print  b      str b   print  c      str c   print  a    b     s     a  b   print  b    c     s     b  c   print  a    c     s     a  c   print  a is b     s     a is b   print  b is c     s     b is c   print  a is c     s     a is c    d   list a  d 1     kiwi  a   tuple d   print  a      str a   print  b      str b   print  c      str c   print  a    b     s     a  b   print  b    c     s     b  c   print  a    c     s     a  c   print  a is b     s     a is b   print  b is c     s     b is c   print  a is c     s     a is c     Yields   a    apple    canana    cherry   b    apple    canana    cherry   c    apple    canana    cherry   a    b    True b    c    True a    c    True a is b    False b is c    False a is c    True a    apple    kiwi    cherry   b    apple    canana    cherry   c    apple    canana    cherry   a    b    False b    c    True a    c    False a is b    False b is c    False a is c    False

User · Answer

based on Jon s Idea and dear Trufa  def modifyTuple tup  oldval  newval       lst list tup      for i in range tup count oldval            index   lst index oldval          lst index  newval      return tuple lst   print modTupByIndex  1  1  3   1   a     it changes all of your old values occurrences

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I  m late to the game but I think the simplest  resource-friendliest and fastest way  depending on the situation   is to overwrite the tuple itself  Since this would remove the need for the list  amp  variable creation and is archived in one line      new   24 t    1  2  3  t    t 0  t 1  new    gt  gt  gt   1  2  24    But  This is only handy for rather small tuples and also limits you to a fixed tuple value  nevertheless  this is the case for tuples most of the time anyway   So in this particular case it would look like this   new    200  t     275    54000    0 0    5000 0    0 0   t    new  t 1   t 2   t 3   t 4     gt  gt  gt    200    54000    0 0    5000 0    0 0

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EDIT  This doesn t work on tuples with duplicate entries yet    Based on Pooya s idea   If you are planning on doing this often  which you shouldn t since tuples are inmutable for a reason  you should do something like this   def modTupByIndex tup  index  ins       return tuple tup 0 index      ins     tuple tup index 1     print modTupByIndex  1 2 3  2  a     Or based on Jon s idea   def modTupByIndex tup  index  ins       lst   list tup      lst index    ins     return tuple lst   print modTupByIndex  1 2 3  1  a

User · Answer

Well  as Trufa has already shown  there are basically two ways of replacing a tuple s element at a given index  Either convert the tuple to a list  replace the element and convert back  or construct a new tuple by concatenation   In  1   def replace at index1 tup  ix  val               lst   list tup              lst ix    val             return tuple lst           In  2   def replace at index2 tup  ix  val               return tup  ix     val     tup ix 1             So  which method is better  that is  faster   It turns out that for short tuples  on Python 3 3   concatenation is actually faster   In  3   d   tuple range 10    In  4    timeit replace at index1 d  5  99  1000000 loops  best of 3  872 ns per loop  In  5    timeit replace at index2 d  5  99  1000000 loops  best of 3  642 ns per loop   Yet if we look at longer tuples  list conversion is the way to go   In  6   k   tuple range 1000    In  7    timeit replace at index1 k  500  99  100000 loops  best of 3  9 08   s per loop  In  8    timeit replace at index2 k  500  99  100000 loops  best of 3  10 1   s per loop   For very long tuples  list conversion is substantially better   In  9   m   tuple range 1000000    In  10    timeit replace at index1 m  500000  99  10 loops  best of 3  26 6 ms per loop  In  11    timeit replace at index2 m  500000  99  10 loops  best of 3  35 9 ms per loop   Also  performance of the concatenation method depends on the index at which we replace the element  For the list method  the index is irrelevant   In  12    timeit replace at index1 m  900000  99  10 loops  best of 3  26 6 ms per loop  In  13    timeit replace at index2 m  900000  99  10 loops  best of 3  49 2 ms per loop   So  If your tuple is short  slice and concatenate  If it s long  do the list conversion

User · Answer

I believe this technically answers the question  but don t do this at home  At the moment  all answers involve creating a new tuple  but you can use ctypes to modify a tuple in-memory  Relying on various implementation details of CPython on a 64-bit system  one way to do this is as follows   def modify tuple t  idx  new value          id  happens to give the memory address in CPython  you may       want to use  ctypes addressof  instead      element ptr    ctypes c longlong  from address id t     3   idx  8      element ptr value   id new value        Manually increment the reference count to  new value  to pretend that       this is not a terrible idea      ref count    ctypes c longlong  from address id new value       ref count value    1  t    10  20  30  modify tuple t  1  50      t is now  10  50  30  modify tuple t  -1  50     Will probably crash your Python runtime

User · Answer

Not that this is superior  but if anyone is curious it can be done on one line with   tuple   tuple  200 if i    0 else   for i    in enumerate tuple

User · Answer

I ve found the best way to edit tuples is to recreate the tuple using the previous version as the base   Here s an example I used for making a lighter version of a colour  I had it open already at the time      colour   tuple  c 50 for c in colour     What it does  is it goes through the tuple  colour  and reads each item  does something to it  and finally adds it to the new tuple   So what you d want would be something like   values     275    54000    0 0    5000 0    0 0    values     tuple for i in values  if i   0  i   200 else i   values i     That specific one doesn t work  but the concept is what you need   tuple    0  1  2       tuple   iterate through tuple  alter each item as needed   that s the concept

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You can change the value of tuple using copy by reference   gt  gt  gt  tuple1  20 30 40    gt  gt  gt  tuple2 tuple1   gt  gt  gt  tuple2      20  30  40    gt  gt  gt  tuple2 1  10   gt  gt  gt  print tuple2       20  10  40    gt  gt  gt  print tuple1       20  10  40

User · Answer

Depending on your problem slicing can be a really neat solution    gt  gt  gt  b    1  2  3  4  5   gt  gt  gt  b  2     8 9    b 3    1  2  8  9  4  5   gt  gt  gt  b  2     8     b 3    1  2  8  4  5    This allows you to add multiple elements or also to replace a few elements  especially if they are  neighbours   In the above case casting to a list is probably more appropriate and readable  even though the slicing notation is much shorter

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You can t   If you want to change it  you need to use a list instead of a tuple   Note that you could instead make a new tuple that has the new value as its first element

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It is possible with a one liner   values     275    54000    0 0    5000 0    0 0   values     300    values 1

User · Answer

First you need to ask  why you want to do this   But it s possible via   t     275    54000    0 0    5000 0    0 0   lst   list t  lst 0     300  t   tuple lst    But if you re going to need to change things  you probably are better off keeping it as a list

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As Hunter McMillen mentioned  tuples are immutable  you need to create a new tuple in order to achieve this  For instance   gt  gt  gt  tpl     275    54000    0 0    5000 0    0 0    gt  gt  gt  change value   200  gt  gt  gt  tpl    change value     tpl 1    gt  gt  gt  tpl  200   54000    0 0    5000 0    0 0

User · Answer

i did this   list    1 2 3 4 5  tuple    list    and to change  just do  list 0  6   and u can change a tuple  D  here is it copied exactly from IDLE   gt  gt  gt  list  1 2 3 4 5 6 7 8 9    gt  gt  gt  tuple  list    gt  gt  gt  print tuple    1  2  3  4  5  6  7  8  9    gt  gt  gt  list 0  6   gt  gt  gt  print tuple    6  2  3  4  5  6  7  8  9

User · Answer

You can t modify items in tuple  but you can modify properties of mutable objects in tuples  for example if those objects are lists or actual class objects  For example my list    1 2  tuple of lists    my list  hello   print tuple of lists      1  2    hello   my list 0    0 print tuple of lists      0  2    hello

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Frist  ask yourself why you want to mutate your tuple  There is a reason why strings and tuple are immutable in Ptyhon  if you want to mutate your tuple then it should probably be a list instead    Second  if you still wish to mutate your tuple then you can convert your tuple to a list then convert it back  and reassign the new tuple to the same variable  This is great if you are only going to mutate your tuple once  Otherwise  I personally think that is counterintuitive  Because It is essentially creating a new tuple and every time if you wish to mutate the tuple you would have to perform the conversion  Also If you read the code it would be confusing to think why not just create a list  But it is nice because it doesn t require any library   I suggest using mutabletuple typename  field names  default MtNoDefault  from mutabletuple 0 2  I personally think this way is a more intuitive and readable  The personal reading the code would know that writer intends to mutate this tuple in the future  The downside compares to the list conversion method above is that this requires you to import additional py file   from mutabletuple import mutabletuple  myTuple   mutabletuple  myTuple    v w x y z   p   myTuple  275    54000    0 0    5000 0    0 0   print p v   print 275 p v    200   mutate myTuple print p v   print 200   TL DR  Don t try to mutate tuple  if you do and it is a one-time operation convert tuple to list  mutate it  turn list into a new tuple  and reassign back to the variable holding old tuple  If desires tuple and somehow want to avoid listand want to mutate more than once then create mutabletuple

[python] How to change values in a tuple?

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