Python object deleting itself

Question

Why won t this work   I m trying to make an instance of a class delete itself    gt  gt  gt  class A        def kill self           del self    gt  gt  gt  a   A    gt  gt  gt  a kill    gt  gt  gt  a  lt   main   A instance at 0x01F23170 gt

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I am trying the same thing  I have a RPG battle system in which my Death self  function has to kill the own object of the Fighter class  But it appeared it s not possible  Maybe my class Game in which I collect all participants in the combat should delete units form the  fictional  map        def Death self       if self stats  HP    lt   0          print   s wounds were too much    Dead    self player  Name             del self     else          return True  def Damage self  enemy       todamage   self stats  ATK     randint 1 6      todamage -  enemy stats  DEF       if todamage  gt  0          enemy stats  HP   -  todamage         print   s took  d damage from your attack    enemy player  Name    todamage           enemy Death           return True     else          print  Ineffective              return True def Attack self  enemy       tohit   self stats  DEX     randint 1 6      if tohit  gt  enemy stats  EVA            print  You landed a successful attack on  s    enemy player  Name             self Damage enemy          return True     else          print  Miss            return True def Action self  enemylist       for i in range 0  len enemylist            print  No  d   r   i  enemylist i        print  It s your turn   s  Take action    self player  Name         choice   input   n A ttack n D efend n S kill n I tem n H elp n gt        if choice     a or choice     A           who   int input  Who              self Attack enemylist who           return True     else          return self Action

User · Answer

This is something I have done in the past  Create a list of objects  and you can then have objects delete themselves with the list remove   method   bullet list       class Bullet      def kill self self           bullet list remove self   bullet list     Bullet

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I can t tell you how this is possible with classes  but functions can delete themselves    def kill self exit msg    killed        global kill self     del kill self     return exit msg   And see the output     gt  gt  gt  kill self  lt function kill self at 0x02A2C780 gt   gt  gt  gt  kill self    killed   gt  gt  gt  kill self Traceback  most recent call last     File   lt pyshell 28 gt    line 1  in  lt module gt      kill self NameError  name  kill self  is not defined   I don t think that deleting an individual instance of a class without knowing the name of it is possible    NOTE  If you assign another name to the function  the other name will still reference the old one  but will cause errors once you attempt to run it    gt  gt  gt  x   kill self  gt  gt  gt  kill self    gt  gt  gt  kill self NameError  name  kill self  is not defined  gt  gt  gt  x  lt function kill self at 0x    gt   gt  gt  gt  x   NameError  global name  kill self  is not defined

User · Answer

Indeed  Python does garbage collection through reference counting  As soon as the last reference to an object falls out of scope  it is deleted  In your example   a   A   a kill     I don t believe there s any way for variable  a  to implicitly set itself to None

User · Answer

Indeed  Python does garbage collection through reference counting  As soon as the last reference to an object falls out of scope  it is deleted  In your example   a   A   a kill     I don t believe there s any way for variable  a  to implicitly set itself to None

User · Answer

class A    def   init   self  function       self function   function   def kill self       self function self   def delete object                           We are no longer in A object   del object  a   A delete  print a  a kill   print a    May this code work

User · Answer

Indeed  Python does garbage collection through reference counting  As soon as the last reference to an object falls out of scope  it is deleted  In your example   a   A   a kill     I don t believe there s any way for variable  a  to implicitly set itself to None

User · Answer

what you could do is take the name with you in the class and make a dictionairy   class A    def   init   self  name       self name name   def kill self      del dict self name   dict    dict  a   A  a   dict  a   kill

User · Answer

I m curious as to why you would want to do such a thing   Chances are  you should just let garbage collection do its job   In python  garbage collection is pretty deterministic   So you don t really have to worry as much about just leaving objects laying around in memory like you would in other languages  not to say that refcounting doesn t have disadvantages    Although one thing that you should consider is a wrapper around any objects or resources you may get rid of later   class foo object       def   init   self           self some big object   some resource      def killBigObject self           del some big object   In response to Null s addendum   Unfortunately  I don t believe there s a way to do what you want to do the way you want to do it   Here s one way that you may wish to consider    gt  gt  gt  class manager object           def   init   self                   self lookup              def addItem self  name  item                   self lookup name    item                 item setLookup self lookup   gt  gt  gt  class Item object           def   init   self  name                   self name   name         def setLookup self  lookup                   self lookup   lookup         def deleteSelf self                   del self lookup self name   gt  gt  gt  man   manager    gt  gt  gt  item   Item  foo    gt  gt  gt  man addItem  foo   item   gt  gt  gt  man lookup    foo    lt   main   Item object at 0x81b50 gt    gt  gt  gt  item deleteSelf    gt  gt  gt  man lookup       It s a little bit messy  but that should give you the idea   Essentially  I don t think that tying an item s existence in the game to whether or not it s allocated in memory is a good idea   This is because the conditions for the item to be garbage collected are probably going to be different than what the conditions are for the item in the game   This way  you don t have to worry so much about that

User · Answer

self  is only a reference to the object   del self  is deleting the  self  reference from the local namespace of the kill function  instead of the actual object   To see this for yourself  look at what happens when these two functions are executed    gt  gt  gt  class A            def kill a self               print self             del self         def kill b self               del self             print self       gt  gt  gt  a   A    gt  gt  gt  b   A    gt  gt  gt  a kill a    lt   main   A instance at 0xb771250c gt   gt  gt  gt  b kill b   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 7  in kill b UnboundLocalError  local variable  self  referenced before assignment

User · Answer

You don t need to use del to delete instances in the first place   Once the last reference to an object is gone  the object will be garbage collected   Maybe you should tell us more about the full problem

User · Answer

In this specific context  your example doesn t make a lot of sense   When a Being picks up an Item  the item retains an individual existence   It doesn t disappear because it s been picked up   It still exists  but it s  a  in the same location as the Being  and  b  no longer eligible to be picked up   While it s had a state change  it still exists   There is a two-way association between Being and Item   The Being has the Item in a collection   The Item is associated with a Being   When an Item is picked up by a Being  two things have to happen    The Being how adds the Item in some set of items   Your bag attribute  for example  could be such a set    A list is a poor choice -- does order matter in the bag   The Item s location changes from where it used to be to the Being s location   There are probably two classes os Items - those with an independent sense of location  because they move around by themselves  and items that have to delegate location to the Being or Place where they re sitting    Under no circumstances does any Python object ever need to get deleted   If an item is  destroyed   then it s not in a Being s bag   It s not in a location     player bag remove cat    Is all that s required to let the cat out of the bag   Since the cat is not used anywhere else  it will both exist as  used  memory and not exist because nothing in your program can access it    It will quietly vanish from memory when some quantum event occurs and memory references are garbage collected   On the other hand   here add  cat   player bag remove cat    Will put the cat in the current location   The cat continues to exist  and will not be put out with the garbage

User · Answer

I m curious as to why you would want to do such a thing   Chances are  you should just let garbage collection do its job   In python  garbage collection is pretty deterministic   So you don t really have to worry as much about just leaving objects laying around in memory like you would in other languages  not to say that refcounting doesn t have disadvantages    Although one thing that you should consider is a wrapper around any objects or resources you may get rid of later   class foo object       def   init   self           self some big object   some resource      def killBigObject self           del some big object   In response to Null s addendum   Unfortunately  I don t believe there s a way to do what you want to do the way you want to do it   Here s one way that you may wish to consider    gt  gt  gt  class manager object           def   init   self                   self lookup              def addItem self  name  item                   self lookup name    item                 item setLookup self lookup   gt  gt  gt  class Item object           def   init   self  name                   self name   name         def setLookup self  lookup                   self lookup   lookup         def deleteSelf self                   del self lookup self name   gt  gt  gt  man   manager    gt  gt  gt  item   Item  foo    gt  gt  gt  man addItem  foo   item   gt  gt  gt  man lookup    foo    lt   main   Item object at 0x81b50 gt    gt  gt  gt  item deleteSelf    gt  gt  gt  man lookup       It s a little bit messy  but that should give you the idea   Essentially  I don t think that tying an item s existence in the game to whether or not it s allocated in memory is a good idea   This is because the conditions for the item to be garbage collected are probably going to be different than what the conditions are for the item in the game   This way  you don t have to worry so much about that

User · Answer

If you re using a single reference to the object  then the object can kill itself by resetting that outside reference to itself  as in   class Zero      pOne   None  class One       pTwo   None         def process self           self pTwo   Two           self pTwo dothing           self pTwo kill              now this fails          self pTwo dothing     class Two       def dothing self           print  two says  doing something       def kill self           Zero pOne pTwo   None   def main        Zero pOne   One     just a global     Zero pOne process     if   name       main         main     You can of course do the logic control by checking for the object existence from outside the object  rather than object state   as for instance in   if object exists     use existing obj   else      obj   Obj

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Realistically you should not need to delete the object to do what you are trying to do  Instead you can change the state of the object   An example of how this works without getting into the coding would be your player fighting a monster and killing the monster  The state of this monster is fighting  The monster will be accessing all methods needed for fighting  When the monster dies because his health drops to 0  the monsters state will change to dead and your character will stop attacking automatically   This methodology is very similar to using flags or even keywords   Also apparently in python deleting classes is not required since they will be garbage collected automatically when they are not used anymore

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I think I ve finally got it  NOTE  You should not use this in normal code  but it is possible  This is only meant as a curiosity  see other answers for real-world solutions to this problem   Take a look at this code     NOTE  This is Python 3 code  it should work with python 2  but I haven t tested it  import weakref  class InsaneClass object        alive          def   new   cls           self   super     new   cls          InsaneClass  alive append self           return weakref proxy self       def commit suicide self           self  alive remove self   instance   InsaneClass   instance commit suicide   print instance     Raises Error  ReferenceError  weakly-referenced object no longer exists   When the object is created in the   new   method  the instance is replaced by a weak reference proxy and the only strong reference is kept in the  alive class attribute   What is a weak-reference   Weak-reference is a reference which does not count as a reference when the garbage collector collects the object  Consider this example    gt  gt  gt  class Test    pass   gt  gt  gt  a   Test    gt  gt  gt  b   Test     gt  gt  gt  c   a  gt  gt  gt  d   weakref proxy b   gt  gt  gt  d  lt weakproxy at 0x10671ae58 to Test at 0x10670f4e0 gt     The weak reference points to the Test   object   gt  gt  gt  del a  gt  gt  gt  c  lt   main   Test object at 0x10670f390 gt    c still exists   gt  gt  gt  del b  gt  gt  gt  d  lt weakproxy at 0x10671ab38 to NoneType at 0x1002050d0 gt     d is now only a weak-reference to None  The Test   instance was garbage-collected   So the only strong reference to the instance is stored in the  alive class attribute  And when the commit suicide   method removes the reference the instance is garbage-collected

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I think I ve finally got it  NOTE  You should not use this in normal code  but it is possible  This is only meant as a curiosity  see other answers for real-world solutions to this problem   Take a look at this code     NOTE  This is Python 3 code  it should work with python 2  but I haven t tested it  import weakref  class InsaneClass object        alive          def   new   cls           self   super     new   cls          InsaneClass  alive append self           return weakref proxy self       def commit suicide self           self  alive remove self   instance   InsaneClass   instance commit suicide   print instance     Raises Error  ReferenceError  weakly-referenced object no longer exists   When the object is created in the   new   method  the instance is replaced by a weak reference proxy and the only strong reference is kept in the  alive class attribute   What is a weak-reference   Weak-reference is a reference which does not count as a reference when the garbage collector collects the object  Consider this example    gt  gt  gt  class Test    pass   gt  gt  gt  a   Test    gt  gt  gt  b   Test     gt  gt  gt  c   a  gt  gt  gt  d   weakref proxy b   gt  gt  gt  d  lt weakproxy at 0x10671ae58 to Test at 0x10670f4e0 gt     The weak reference points to the Test   object   gt  gt  gt  del a  gt  gt  gt  c  lt   main   Test object at 0x10670f390 gt    c still exists   gt  gt  gt  del b  gt  gt  gt  d  lt weakproxy at 0x10671ab38 to NoneType at 0x1002050d0 gt     d is now only a weak-reference to None  The Test   instance was garbage-collected   So the only strong reference to the instance is stored in the  alive class attribute  And when the commit suicide   method removes the reference the instance is garbage-collected

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class A    def   init   self  function       self function   function   def kill self       self function self   def delete object                           We are no longer in A object   del object  a   A delete  print a  a kill   print a    May this code work

User · Answer

I m curious as to why you would want to do such a thing   Chances are  you should just let garbage collection do its job   In python  garbage collection is pretty deterministic   So you don t really have to worry as much about just leaving objects laying around in memory like you would in other languages  not to say that refcounting doesn t have disadvantages    Although one thing that you should consider is a wrapper around any objects or resources you may get rid of later   class foo object       def   init   self           self some big object   some resource      def killBigObject self           del some big object   In response to Null s addendum   Unfortunately  I don t believe there s a way to do what you want to do the way you want to do it   Here s one way that you may wish to consider    gt  gt  gt  class manager object           def   init   self                   self lookup              def addItem self  name  item                   self lookup name    item                 item setLookup self lookup   gt  gt  gt  class Item object           def   init   self  name                   self name   name         def setLookup self  lookup                   self lookup   lookup         def deleteSelf self                   del self lookup self name   gt  gt  gt  man   manager    gt  gt  gt  item   Item  foo    gt  gt  gt  man addItem  foo   item   gt  gt  gt  man lookup    foo    lt   main   Item object at 0x81b50 gt    gt  gt  gt  item deleteSelf    gt  gt  gt  man lookup       It s a little bit messy  but that should give you the idea   Essentially  I don t think that tying an item s existence in the game to whether or not it s allocated in memory is a good idea   This is because the conditions for the item to be garbage collected are probably going to be different than what the conditions are for the item in the game   This way  you don t have to worry so much about that

User · Answer

In this specific context  your example doesn t make a lot of sense   When a Being picks up an Item  the item retains an individual existence   It doesn t disappear because it s been picked up   It still exists  but it s  a  in the same location as the Being  and  b  no longer eligible to be picked up   While it s had a state change  it still exists   There is a two-way association between Being and Item   The Being has the Item in a collection   The Item is associated with a Being   When an Item is picked up by a Being  two things have to happen    The Being how adds the Item in some set of items   Your bag attribute  for example  could be such a set    A list is a poor choice -- does order matter in the bag   The Item s location changes from where it used to be to the Being s location   There are probably two classes os Items - those with an independent sense of location  because they move around by themselves  and items that have to delegate location to the Being or Place where they re sitting    Under no circumstances does any Python object ever need to get deleted   If an item is  destroyed   then it s not in a Being s bag   It s not in a location     player bag remove cat    Is all that s required to let the cat out of the bag   Since the cat is not used anywhere else  it will both exist as  used  memory and not exist because nothing in your program can access it    It will quietly vanish from memory when some quantum event occurs and memory references are garbage collected   On the other hand   here add  cat   player bag remove cat    Will put the cat in the current location   The cat continues to exist  and will not be put out with the garbage

User · Answer

You don t need to use del to delete instances in the first place   Once the last reference to an object is gone  the object will be garbage collected   Maybe you should tell us more about the full problem

User · Answer

You don t need to use del to delete instances in the first place   Once the last reference to an object is gone  the object will be garbage collected   Maybe you should tell us more about the full problem

User · Answer

what you could do is take the name with you in the class and make a dictionairy   class A    def   init   self  name       self name name   def kill self      del dict self name   dict    dict  a   A  a   dict  a   kill

User · Answer

You don t need to use del to delete instances in the first place   Once the last reference to an object is gone  the object will be garbage collected   Maybe you should tell us more about the full problem

User · Answer

Realistically you should not need to delete the object to do what you are trying to do  Instead you can change the state of the object   An example of how this works without getting into the coding would be your player fighting a monster and killing the monster  The state of this monster is fighting  The monster will be accessing all methods needed for fighting  When the monster dies because his health drops to 0  the monsters state will change to dead and your character will stop attacking automatically   This methodology is very similar to using flags or even keywords   Also apparently in python deleting classes is not required since they will be garbage collected automatically when they are not used anymore

User · Answer

I am trying the same thing  I have a RPG battle system in which my Death self  function has to kill the own object of the Fighter class  But it appeared it s not possible  Maybe my class Game in which I collect all participants in the combat should delete units form the  fictional  map        def Death self       if self stats  HP    lt   0          print   s wounds were too much    Dead    self player  Name             del self     else          return True  def Damage self  enemy       todamage   self stats  ATK     randint 1 6      todamage -  enemy stats  DEF       if todamage  gt  0          enemy stats  HP   -  todamage         print   s took  d damage from your attack    enemy player  Name    todamage           enemy Death           return True     else          print  Ineffective              return True def Attack self  enemy       tohit   self stats  DEX     randint 1 6      if tohit  gt  enemy stats  EVA            print  You landed a successful attack on  s    enemy player  Name             self Damage enemy          return True     else          print  Miss            return True def Action self  enemylist       for i in range 0  len enemylist            print  No  d   r   i  enemylist i        print  It s your turn   s  Take action    self player  Name         choice   input   n A ttack n D efend n S kill n I tem n H elp n gt        if choice     a or choice     A           who   int input  Who              self Attack enemylist who           return True     else          return self Action

User · Answer

I can t tell you how this is possible with classes  but functions can delete themselves    def kill self exit msg    killed        global kill self     del kill self     return exit msg   And see the output     gt  gt  gt  kill self  lt function kill self at 0x02A2C780 gt   gt  gt  gt  kill self    killed   gt  gt  gt  kill self Traceback  most recent call last     File   lt pyshell 28 gt    line 1  in  lt module gt      kill self NameError  name  kill self  is not defined   I don t think that deleting an individual instance of a class without knowing the name of it is possible    NOTE  If you assign another name to the function  the other name will still reference the old one  but will cause errors once you attempt to run it    gt  gt  gt  x   kill self  gt  gt  gt  kill self    gt  gt  gt  kill self NameError  name  kill self  is not defined  gt  gt  gt  x  lt function kill self at 0x    gt   gt  gt  gt  x   NameError  global name  kill self  is not defined

User · Answer

A replacement implement  class A       def   init   self           self a   123      def kill self           from itertools import chain         for attr name in chain dir self   class     dir self                if attr name startswith                        continue             attr   getattr self  attr name              if callable attr                   setattr self  attr name  lambda  args    kwargs  print  NoneType                else                  setattr self  attr name  None          a   str     lambda             a   repr     lambda      a   A   print a a  a kill    print a a  a kill    a   A   print a a   will outputs  123 None NoneType 123

User · Answer

self  is only a reference to the object   del self  is deleting the  self  reference from the local namespace of the kill function  instead of the actual object   To see this for yourself  look at what happens when these two functions are executed    gt  gt  gt  class A            def kill a self               print self             del self         def kill b self               del self             print self       gt  gt  gt  a   A    gt  gt  gt  b   A    gt  gt  gt  a kill a    lt   main   A instance at 0xb771250c gt   gt  gt  gt  b kill b   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 7  in kill b UnboundLocalError  local variable  self  referenced before assignment

User · Answer

self  is only a reference to the object   del self  is deleting the  self  reference from the local namespace of the kill function  instead of the actual object   To see this for yourself  look at what happens when these two functions are executed    gt  gt  gt  class A            def kill a self               print self             del self         def kill b self               del self             print self       gt  gt  gt  a   A    gt  gt  gt  b   A    gt  gt  gt  a kill a    lt   main   A instance at 0xb771250c gt   gt  gt  gt  b kill b   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 7  in kill b UnboundLocalError  local variable  self  referenced before assignment

User · Answer

I m curious as to why you would want to do such a thing   Chances are  you should just let garbage collection do its job   In python  garbage collection is pretty deterministic   So you don t really have to worry as much about just leaving objects laying around in memory like you would in other languages  not to say that refcounting doesn t have disadvantages    Although one thing that you should consider is a wrapper around any objects or resources you may get rid of later   class foo object       def   init   self           self some big object   some resource      def killBigObject self           del some big object   In response to Null s addendum   Unfortunately  I don t believe there s a way to do what you want to do the way you want to do it   Here s one way that you may wish to consider    gt  gt  gt  class manager object           def   init   self                   self lookup              def addItem self  name  item                   self lookup name    item                 item setLookup self lookup   gt  gt  gt  class Item object           def   init   self  name                   self name   name         def setLookup self  lookup                   self lookup   lookup         def deleteSelf self                   del self lookup self name   gt  gt  gt  man   manager    gt  gt  gt  item   Item  foo    gt  gt  gt  man addItem  foo   item   gt  gt  gt  man lookup    foo    lt   main   Item object at 0x81b50 gt    gt  gt  gt  item deleteSelf    gt  gt  gt  man lookup       It s a little bit messy  but that should give you the idea   Essentially  I don t think that tying an item s existence in the game to whether or not it s allocated in memory is a good idea   This is because the conditions for the item to be garbage collected are probably going to be different than what the conditions are for the item in the game   This way  you don t have to worry so much about that

User · Answer

In this specific context  your example doesn t make a lot of sense   When a Being picks up an Item  the item retains an individual existence   It doesn t disappear because it s been picked up   It still exists  but it s  a  in the same location as the Being  and  b  no longer eligible to be picked up   While it s had a state change  it still exists   There is a two-way association between Being and Item   The Being has the Item in a collection   The Item is associated with a Being   When an Item is picked up by a Being  two things have to happen    The Being how adds the Item in some set of items   Your bag attribute  for example  could be such a set    A list is a poor choice -- does order matter in the bag   The Item s location changes from where it used to be to the Being s location   There are probably two classes os Items - those with an independent sense of location  because they move around by themselves  and items that have to delegate location to the Being or Place where they re sitting    Under no circumstances does any Python object ever need to get deleted   If an item is  destroyed   then it s not in a Being s bag   It s not in a location     player bag remove cat    Is all that s required to let the cat out of the bag   Since the cat is not used anywhere else  it will both exist as  used  memory and not exist because nothing in your program can access it    It will quietly vanish from memory when some quantum event occurs and memory references are garbage collected   On the other hand   here add  cat   player bag remove cat    Will put the cat in the current location   The cat continues to exist  and will not be put out with the garbage

User · Answer

Indeed  Python does garbage collection through reference counting  As soon as the last reference to an object falls out of scope  it is deleted  In your example   a   A   a kill     I don t believe there s any way for variable  a  to implicitly set itself to None

User · Answer

If you re using a single reference to the object  then the object can kill itself by resetting that outside reference to itself  as in   class Zero      pOne   None  class One       pTwo   None         def process self           self pTwo   Two           self pTwo dothing           self pTwo kill              now this fails          self pTwo dothing     class Two       def dothing self           print  two says  doing something       def kill self           Zero pOne pTwo   None   def main        Zero pOne   One     just a global     Zero pOne process     if   name       main         main     You can of course do the logic control by checking for the object existence from outside the object  rather than object state   as for instance in   if object exists     use existing obj   else      obj   Obj

User · Answer

In this specific context  your example doesn t make a lot of sense   When a Being picks up an Item  the item retains an individual existence   It doesn t disappear because it s been picked up   It still exists  but it s  a  in the same location as the Being  and  b  no longer eligible to be picked up   While it s had a state change  it still exists   There is a two-way association between Being and Item   The Being has the Item in a collection   The Item is associated with a Being   When an Item is picked up by a Being  two things have to happen    The Being how adds the Item in some set of items   Your bag attribute  for example  could be such a set    A list is a poor choice -- does order matter in the bag   The Item s location changes from where it used to be to the Being s location   There are probably two classes os Items - those with an independent sense of location  because they move around by themselves  and items that have to delegate location to the Being or Place where they re sitting    Under no circumstances does any Python object ever need to get deleted   If an item is  destroyed   then it s not in a Being s bag   It s not in a location     player bag remove cat    Is all that s required to let the cat out of the bag   Since the cat is not used anywhere else  it will both exist as  used  memory and not exist because nothing in your program can access it    It will quietly vanish from memory when some quantum event occurs and memory references are garbage collected   On the other hand   here add  cat   player bag remove cat    Will put the cat in the current location   The cat continues to exist  and will not be put out with the garbage

User · Answer

This is something I have done in the past  Create a list of objects  and you can then have objects delete themselves with the list remove   method   bullet list       class Bullet      def kill self self           bullet list remove self   bullet list     Bullet

User · Answer

A replacement implement  class A       def   init   self           self a   123      def kill self           from itertools import chain         for attr name in chain dir self   class     dir self                if attr name startswith                        continue             attr   getattr self  attr name              if callable attr                   setattr self  attr name  lambda  args    kwargs  print  NoneType                else                  setattr self  attr name  None          a   str     lambda             a   repr     lambda      a   A   print a a  a kill    print a a  a kill    a   A   print a a   will outputs  123 None NoneType 123

User · Answer

self  is only a reference to the object   del self  is deleting the  self  reference from the local namespace of the kill function  instead of the actual object   To see this for yourself  look at what happens when these two functions are executed    gt  gt  gt  class A            def kill a self               print self             del self         def kill b self               del self             print self       gt  gt  gt  a   A    gt  gt  gt  b   A    gt  gt  gt  a kill a    lt   main   A instance at 0xb771250c gt   gt  gt  gt  b kill b   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 7  in kill b UnboundLocalError  local variable  self  referenced before assignment

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