How to create a custom string representation for a class object

Question

Consider this class   class foo object       pass   The default string representation looks something like this    gt  gt  gt  str foo    lt class    main   foo  gt     How can I make this display a custom string

User · Answer

class foo object       def   str   self           return  representation      def   unicode   self           return u representation

User · Answer

Implement   str     or   repr     in the class s metaclass  class MC type     def   repr   self       return  Wahaha    class C object       metaclass     MC  print C  Use   str   if you mean a readable stringification  use   repr   for unambiguous representations

User · Answer

If you have to choose between   repr   or   str   go for the first one  as by default implementation   str   calls   repr   when it wasn t defined    Custom Vector3 example   class Vector3 object       def   init   self  args           self x   args 0          self y   args 1          self z   args 2       def   repr   self           return  Vector3   0   1   2     format self x  self y  self z       def   str   self           return  x   0   y   1   z   2   format self x  self y  self z    In this example  repr returns again a string that can be directly consumed executed  whereas str is more useful as a debug output    v   Vector3  1 2 3   print repr v      Vector3  1 2 3   print str v       x 1  y 2  z 3

User · Answer

Just adding to all the fine answers  my version with decoration   from   future   import print function import six  def classrep rep       def decorate cls           class RepMetaclass type               def   repr   self                   return rep          class Decorated six with metaclass RepMetaclass  cls                pass          return Decorated     return decorate    classrep  Wahaha    class C object       pass  print C    stdout   Wahaha    The down sides    You can t declare C without a super class  no class C   C instances will be instances of some strange derivation  so it s probably a good idea to add a   repr   for the instances as well

User · Answer

Ignacio Vazquez-Abrams  approved answer is quite right  It is  however  from the Python 2 generation  An update for the now-current Python 3 would be      class MC type     def   repr   self       return  Wahaha    class C object  metaclass MC       pass  print C    If you want code that runs across both Python 2 and Python 3  the six module has you covered   from   future   import print function from six import with metaclass  class MC type     def   repr   self       return  Wahaha    class C with metaclass MC        pass  print C    Finally  if you have one class that you want to have a custom static repr  the class-based approach above works great  But if you have several  you d have to generate a metaclass similar to MC for each  and that can get tiresome  In that case  taking your metaprogramming one step further and creating a metaclass factory makes things a bit cleaner   from   future   import print function from six import with metaclass  def custom class repr name               Factory that returns custom metaclass with a class     repr     that     returns   name                return type  whatever    type        repr     lambda self  name    class C with metaclass custom class repr  Wahaha       pass  class D with metaclass custom class repr  Booyah       pass  class E with metaclass custom class repr  Gotcha       pass  print C  D  E    prints   Wahaha  Booyah  Gotcha    Metaprogramming isn t something you generally need everyday mdash but when you need it  it really hits the spot

[python] How to create a custom string representation for a class object?

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