Add an object to a python list

Question

I am trying to add an object to a list but since I m adding the actual object when I try to reset the list thereafter  all the values in the list are reset  Is there an actual way how I can add a monitor object to the list and change the values and not affect the ones I ve already saved in the list   Thanks  Code   arrayList       for x in allValues            result   model x           arrayList append wM           wM reset     where wM is a monitor class - which is being calculated   worked out in the model method

User · Accepted Answer

Is your problem similar to this   l     0     4 l 0  0     1 print l   prints    1    1    1    1      If so  you simply need to copy the objects when you store them   import copy l    copy copy x  for x in   0     4  l 0  0     1 print l   prints    1    0    0    0      The objects in question should implement a   copy   method to copy objects  See the documentation for copy  You may also be interested in copy deepcopy  which is there as well   EDIT  Here s the problem   arrayList      for x in allValues      result   model x      arrayList append wM    appends the wM object to the list     wM reset               clears  the wM object   You need to append a copy   import copy arrayList      for x in allValues      result   model x      arrayList append copy copy wM     appends a copy to the list     wM reset                          clears the wM object   But I m still confused as to where wM is coming from  Won t you just be copying the same wM object over and over  except clearing it after the first time so all the rest will be empty  Or does model   modify the wM  which sounds like a terrible design flaw to me   And why are you throwing away result

User · Answer

while you should show how your code looks like that gives the problem  i think this scenario is very common  See copy deepcopy

User · Answer

If i am correct in believing that you are adding a variable to the array but when you change that variable outside of the array  it also changes inside the array but you don t want it to then it is a really simple solution   When you are saving the variable to the array you should turn it into a string by simply putting str variablename   For example   array append str variablename     Using this method your code should look like this   arrayList      for x in allValues      result   model x      arrayList append str wM           this is the only line that is changed      wM reset

User · Answer

You need to create a copy of the list before you modify its contents   A quick shortcut to duplicate a list is this   mylist      Example    gt  gt  gt  first    1 2 3   gt  gt  gt  second   first     gt  gt  gt  second append 4   gt  gt  gt  first  1  2  3   gt  gt  gt  second  1  2  3  4    And to show the default behavior that would modify the orignal list  since a name in Python is just a reference to the underlying object     gt  gt  gt  first    1 2 3   gt  gt  gt  second   first  gt  gt  gt  second append 4   gt  gt  gt  first  1  2  3  4   gt  gt  gt  second  1  2  3  4    Note that this only works for lists  If you need to duplicate the contents of a dictionary  you must use copy deepcopy   as suggested by others

[python] Add an object to a python list

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