calling a function from class in python - different way

Question

EDIT2  Thank you all for your help  EDIT  on adding  staticmethod  it works  However I am still wondering why i am getting a type error here    I have just started OOPS and am completely new to it  I have a very basic question regarding the different ways I can call a function from a class  I have a testClass py file with the code   class MathsOperations      def   init    self  x  y           self a   x         self b   y     def testAddition  self           return  self a   self b       def testMultiplication  self           return  self a   self b    I am calling this class from another file called main py with the following code   from testClass import MathsOperations  xyz   MathsOperations 2  3  print xyz testAddition     This works without any issues  However  I wanted to use the class in a much simpler way   I have now put the following code in the testClass py file  I have dropped the init function this time   class MathsOperations      def testAddition  x  y           return x   y      def testMultiplication  a  b           return a   b   calling this using   from testClass import MathsOperations xyz   MathsOperations   print xyz testAddition 2  3    this doesn t works  Can someone explain what is happening wrongly in case 2  How do I use this class   The error i get is  TypeError  testAddition   takes exactly 2 arguments  3 given

User · Answer

disclaimer  this is not a just to the point answer  it s more like a piece of advice  even if the answer can be found on the references  IMHO  object oriented programming in Python sucks quite a lot   The method dispatching is not very straightforward  you need to know about bound unbound instance class  and static   methods  you can have multiple inheritance and need to deal with legacy and new style classes  yours was old style  and know how the MRO works  properties      In brief  too complex  with lots of things happening under the hood  Let me even say  it is unpythonic  as there are many different ways to achieve the same things   My advice  use OOP only when it s really useful  Usually this means writing classes that implement well known protocols and integrate seamlessly with the rest of the system  Do not create lots of classes just for the sake of writing object oriented code   Take a good read to this pages    http   docs python org reference datamodel html http   docs python org tutorial classes html   you ll find them quite useful   If you really want to learn OOP  I d suggest starting with a more conventional language  like Java  It s not half as fun as Python  but it s more predictable

User · Answer

You need to have an instance of a class to use its methods  Or if you don t need to access any of classes  variables  not static parameters  then you can define the method as static and it can be used even if the class isn t instantiated  Just add  staticmethod decorator to your methods   class MathsOperations       staticmethod     def testAddition  x  y           return x   y      staticmethod     def testMultiplication  a  b           return a   b   docs  http   docs python org library functions html staticmethod

User · Answer

class MathsOperations      def   init    self  x  y           self a   x         self b   y     def testAddition  self           return  self a   self b       def testMultiplication  self           return  self a   self b    then  temp   MathsOperations   print temp testAddition

User · Answer

you have to use self as the first parameters of a method  in the second case you should use  class MathOperations      def testAddition  self x  y           return x   y      def testMultiplication  self a  b           return a   b   and in your code you could do the following  tmp   MathOperations print tmp testAddition 2 3    if you use the  class without instantiating a variable first  print MathOperation testAddtion 2 3    it gives you an error  TypeError  unbound method   if you want to do that you will need the  staticmethod decorator  For example    class MathsOperations       staticmethod     def testAddition  x  y           return x   y       staticmethod     def testMultiplication  a  b           return a   b   then in your code you could use  print MathsOperations testAddition 2 3

User · Answer

Your methods don t refer to an object  that is  self   so you should use the  staticmethod decorator   class MathsOperations       staticmethod     def testAddition  x  y           return x   y       staticmethod     def testMultiplication  a  b           return a   b

[python] calling a function from class in python - different way

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