unbound method f must be called with fibo instance as first argument got classobj instance instead

Question

In Python  I m trying to run a method in a class and I get an error   Traceback  most recent call last     File  C  Users domenico Desktop py main py   line 8  in  lt module gt      fibo f     TypeError  unbound method f   must be called with fibo instance    as first argument  got nothing instead    Code   swineflu py   class fibo      a 0     b 0      def f self a 0           print fibo b a         b a          return self a 1    Script main py  import swineflu  f   swineflu fibo   f fibo  fibo f               TypeError is thrown here   What does this error mean  What is causing this error

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In Python 2  3 has different syntax    What if you can t instantiate your Parent class before you need to call one of its methods   Use super ChildClass  self  method   to access parent methods   class ParentClass object       def method to call self  arg 1           print arg 1  class ChildClass ParentClass       def do thing self           super ChildClass  self  method to call  my arg

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How to reproduce this error with as few lines as possible    gt  gt  gt  class C        def f self           print  hi       gt  gt  gt  C f   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unbound method f   must be called with C instance as  first argument  got nothing instead    It fails because of TypeError because you didn t instantiate the class first  you have two choices  1  either make the method static so you can run it in a static way  or 2  instantiate your class so you have an instance to grab onto  to run the method   It looks like you want to run the method in a static way  do this    gt  gt  gt  class C         staticmethod       def f            print  hi       gt  gt  gt  C f   hi   Or  what you probably meant is to use the instantiated instance like this    gt  gt  gt  class C        def f self           print  hi       gt  gt  gt  c1   C    gt  gt  gt  c1 f   hi  gt  gt  gt  C   f   hi   If this confuses you  ask these questions    What is the difference between the behavior of a static method vs the behavior of a normal method  What does it mean to instantiate a class  Differences between how static methods are run vs normal methods  Differences between class and object

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OK  first of all  you don t have to get a reference to the module into a different name  you already have a reference  from the import  and you can just use it   If you want a different name just use import swineflu as f   Second  you are getting a reference to the class rather than instantiating the class   So this should be   import swineflu  fibo   swineflu fibo      get an instance of the class fibo f                    call the method f of the instance   A bound method is one that is attached to an instance of an object  An unbound method is  of course  one that is not attached to an instance  The error usually means you are calling the method on the class rather than on an instance  which is exactly what was happening in this case because you hadn t instantiated the class

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Differences in In python 2 and 3 version   If you already have a default method in a class with same name and you re-declare as a same name  it will appear as unbound-method call of that class instance when you wanted to instantiated it    If you wanted class methods  but you declared them as instance methods instead   An instance method is a method that is used when  to create an instance of the class   An example would be      def user group self      This is an instance method         return  instance method returning group    Class label method       classmethod    def user group groups      This is an class-label method         return  class method returning group    In python 2 and 3 version differ the class  classmethod to write  in python 3 it automatically get that as a class-label method and don t need to write  classmethod  I think this might help you

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f is an  instance  method  However  you are calling it via fibo f  where fibo is the class object  Hence  f is unbound  not bound to any class instance    If you did  a   fibo   a f     then that f is bound  to the instance a

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Try this  For python 2 7 12 we need to define constructor or need to add self to each methods followed by defining an instance of an class called object   import cv2  class calculator       def   init   self    def multiply self  a  b       x  a b     print x   def subtract self  a b       x   a-b     print x   def add self  a b       x   a b     print x   def div self  a b       x   a b     print x    calc   calculator    calc multiply 2 3   calc add 2 3   calc div 10 5   calc subtract 2 3

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fibo   f fibo references the class itself   You probably wanted fibo   f fibo    note the parentheses  to make an instance of the class  after which fibo f   should succeed correctly   f fibo f   fails because you are essentially calling f self  a 0  without supplying self  self is  bound  automatically when you have an instance of the class

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import swineflu  x   swineflu fibo       create an object  x  of class  fibo   an instance of the class x f                     call the method  f     bound to  x      Here is a good tutorial to get started with classes in Python

[python] unbound method f() must be called with fibo_ instance as first argument (got classobj instance instead)

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