Calling a class method raises a TypeError in Python

Question

I don t understand how classes are used  The following code gives me an error when I try to use the class   class MyStuff      def average a  b  c     Get the average of three numbers         result   a   b   c         result   result   3         return result    Now use the function  average  from the  MyStuff  class print MyStuff average 9  18  27     Error   File  class py   line 7  in  lt module gt      print MyStuff average 9  18  27   TypeError  unbound method average   must be called with MyStuff instance as first argument  got int instance instead    What s wrong

User · Accepted Answer

You can instantiate the class by declaring a variable and calling the class as if it were a function:

x = mystuff()
print x.average(9,18,27)

However, this won't work with the code you gave us. When you call a class method on a given object (x), it always passes a pointer to the object as the first parameter when it calls the function. So if you run your code right now, you'll see this error message:

TypeError: average() takes exactly 3 arguments (4 given)

To fix this, you'll need to modify the definition of the average method to take four parameters. The first parameter is an object reference, and the remaining 3 parameters would be for the 3 numbers.

User · Answer

From your example  it seems to me you want to use a static method   class mystuff     staticmethod   def average a b c    get the average of three numbers     result a b c     result result 3     return result  print mystuff average 9 18 27    Please note that an heavy usage of static methods in python is usually a symptom of some bad smell - if you really need functions  then declare them directly on module level

User · Answer

Every function inside a class  and every class variable must take the self argument as pointed   class mystuff      def average a b c    get the average of three numbers             result a b c             result result 3             return result     def sum self a b               return a b   print mystuff average 9 18 27    should raise error print mystuff sum 18 27    should be ok   If class variables are involved    class mystuff      def setVariables self a b               self x   a             self y   b             return a b     def mult self               return x   y    This line will raise an error     def sum self               return self x   self y   print mystuff setVariables 9 18    Setting mystuff x and mystuff y  print mystuff mult     should raise error  print mystuff sum      should be ok

User · Answer

Every function inside a class  and every class variable must take the self argument as pointed   class mystuff      def average a b c    get the average of three numbers             result a b c             result result 3             return result     def sum self a b               return a b   print mystuff average 9 18 27    should raise error print mystuff sum 18 27    should be ok   If class variables are involved    class mystuff      def setVariables self a b               self x   a             self y   b             return a b     def mult self               return x   y    This line will raise an error     def sum self               return self x   self y   print mystuff setVariables 9 18    Setting mystuff x and mystuff y  print mystuff mult     should raise error  print mystuff sum      should be ok

User · Answer

From your example  it seems to me you want to use a static method   class mystuff     staticmethod   def average a b c    get the average of three numbers     result a b c     result result 3     return result  print mystuff average 9 18 27    Please note that an heavy usage of static methods in python is usually a symptom of some bad smell - if you really need functions  then declare them directly on module level

User · Answer

In python member function of a class need explicit self argument  Same as implicit this pointer in C    For more details please check out this page

User · Answer

You need to spend a little more time on some fundamentals of object-oriented programming   This sounds harsh  but it s important    Your class definition is incorrect -- although the syntax happens to be acceptable   The definition is simply wrong   Your use of the class to create an object is entirely missing  Your use of a class to do a calculation is inappropriate   This kind of thing can be done  but it requires the advanced concept of a  staticmehod    Since your example code is wrong in so many ways  you can t get a tidy  fix this  answer   There are too many things to fix   You ll need to look at better examples of class definitions   It s not clear what source material you re using to learn from  but whatever book you re reading is either wrong or incomplete   Please discard whatever book or source you re using and find a better book   Seriously   They ve mislead you on how a class definition looks and how it s used   You might want to look at http   homepage mac com s lott books nonprog htmlchunks pt11 html for a better introduction to classes  objects and Python

User · Answer

From your example  it seems to me you want to use a static method   class mystuff     staticmethod   def average a b c    get the average of three numbers     result a b c     result result 3     return result  print mystuff average 9 18 27    Please note that an heavy usage of static methods in python is usually a symptom of some bad smell - if you really need functions  then declare them directly on module level

User · Answer

In python member function of a class need explicit self argument  Same as implicit this pointer in C    For more details please check out this page

User · Answer

Try this   class mystuff      def average   a b c    get the average of three numbers             result a b c             result result 3             return result   now use the function average from the mystuff class print mystuff average 9 18 27    or this   class mystuff      def average self a b c    get the average of three numbers             result a b c             result result 3             return result   now use the function average from the mystuff class print mystuff average 9 18 27

User · Answer

You need to spend a little more time on some fundamentals of object-oriented programming   This sounds harsh  but it s important    Your class definition is incorrect -- although the syntax happens to be acceptable   The definition is simply wrong   Your use of the class to create an object is entirely missing  Your use of a class to do a calculation is inappropriate   This kind of thing can be done  but it requires the advanced concept of a  staticmehod    Since your example code is wrong in so many ways  you can t get a tidy  fix this  answer   There are too many things to fix   You ll need to look at better examples of class definitions   It s not clear what source material you re using to learn from  but whatever book you re reading is either wrong or incomplete   Please discard whatever book or source you re using and find a better book   Seriously   They ve mislead you on how a class definition looks and how it s used   You might want to look at http   homepage mac com s lott books nonprog htmlchunks pt11 html for a better introduction to classes  objects and Python

User · Answer

Every function inside a class  and every class variable must take the self argument as pointed   class mystuff      def average a b c    get the average of three numbers             result a b c             result result 3             return result     def sum self a b               return a b   print mystuff average 9 18 27    should raise error print mystuff sum 18 27    should be ok   If class variables are involved    class mystuff      def setVariables self a b               self x   a             self y   b             return a b     def mult self               return x   y    This line will raise an error     def sum self               return self x   self y   print mystuff setVariables 9 18    Setting mystuff x and mystuff y  print mystuff mult     should raise error  print mystuff sum      should be ok

User · Answer

In python member function of a class need explicit self argument  Same as implicit this pointer in C    For more details please check out this page

User · Answer

You never created an instance   You ve defined average as an instance method  thus  in order to use average you need to create an instance first

User · Answer

From your example  it seems to me you want to use a static method   class mystuff     staticmethod   def average a b c    get the average of three numbers     result a b c     result result 3     return result  print mystuff average 9 18 27    Please note that an heavy usage of static methods in python is usually a symptom of some bad smell - if you really need functions  then declare them directly on module level

User · Answer

You never created an instance   You ve defined average as an instance method  thus  in order to use average you need to create an instance first

User · Answer

You never created an instance   You ve defined average as an instance method  thus  in order to use average you need to create an instance first

User · Answer

Every function inside a class  and every class variable must take the self argument as pointed   class mystuff      def average a b c    get the average of three numbers             result a b c             result result 3             return result     def sum self a b               return a b   print mystuff average 9 18 27    should raise error print mystuff sum 18 27    should be ok   If class variables are involved    class mystuff      def setVariables self a b               self x   a             self y   b             return a b     def mult self               return x   y    This line will raise an error     def sum self               return self x   self y   print mystuff setVariables 9 18    Setting mystuff x and mystuff y  print mystuff mult     should raise error  print mystuff sum      should be ok

User · Answer

You need to spend a little more time on some fundamentals of object-oriented programming   This sounds harsh  but it s important    Your class definition is incorrect -- although the syntax happens to be acceptable   The definition is simply wrong   Your use of the class to create an object is entirely missing  Your use of a class to do a calculation is inappropriate   This kind of thing can be done  but it requires the advanced concept of a  staticmehod    Since your example code is wrong in so many ways  you can t get a tidy  fix this  answer   There are too many things to fix   You ll need to look at better examples of class definitions   It s not clear what source material you re using to learn from  but whatever book you re reading is either wrong or incomplete   Please discard whatever book or source you re using and find a better book   Seriously   They ve mislead you on how a class definition looks and how it s used   You might want to look at http   homepage mac com s lott books nonprog htmlchunks pt11 html for a better introduction to classes  objects and Python

User · Answer

Try this   class mystuff      def average   a b c    get the average of three numbers             result a b c             result result 3             return result   now use the function average from the mystuff class print mystuff average 9 18 27    or this   class mystuff      def average self a b c    get the average of three numbers             result a b c             result result 3             return result   now use the function average from the mystuff class print mystuff average 9 18 27

User · Answer

In python member function of a class need explicit self argument  Same as implicit this pointer in C    For more details please check out this page

User · Answer

You need to spend a little more time on some fundamentals of object-oriented programming   This sounds harsh  but it s important    Your class definition is incorrect -- although the syntax happens to be acceptable   The definition is simply wrong   Your use of the class to create an object is entirely missing  Your use of a class to do a calculation is inappropriate   This kind of thing can be done  but it requires the advanced concept of a  staticmehod    Since your example code is wrong in so many ways  you can t get a tidy  fix this  answer   There are too many things to fix   You ll need to look at better examples of class definitions   It s not clear what source material you re using to learn from  but whatever book you re reading is either wrong or incomplete   Please discard whatever book or source you re using and find a better book   Seriously   They ve mislead you on how a class definition looks and how it s used   You might want to look at http   homepage mac com s lott books nonprog htmlchunks pt11 html for a better introduction to classes  objects and Python

User · Answer

To minimally modify your example  you could amend the code to   class myclass object           def   init   self     this method creates the class object                  pass          def average self a b c    get the average of three numbers                 result a b c                 result result 3                 return result   mystuff myclass      by default the   init   method is then called        print mystuff average a b c    Or to expand it more fully  allowing you to add other methods   class myclass object           def   init   self a b c                   self a a                 self b b                 self c c         def average self    get the average of three numbers                 result self a self b self c                 result result 3                 return result  a 9 b 18 c 27 mystuff myclass a  b  c          print mystuff average

User · Answer

You never created an instance   You ve defined average as an instance method  thus  in order to use average you need to create an instance first

User · Answer

To minimally modify your example  you could amend the code to   class myclass object           def   init   self     this method creates the class object                  pass          def average self a b c    get the average of three numbers                 result a b c                 result result 3                 return result   mystuff myclass      by default the   init   method is then called        print mystuff average a b c    Or to expand it more fully  allowing you to add other methods   class myclass object           def   init   self a b c                   self a a                 self b b                 self c c         def average self    get the average of three numbers                 result self a self b self c                 result result 3                 return result  a 9 b 18 c 27 mystuff myclass a  b  c          print mystuff average

[python] Calling a class method raises a TypeError in Python

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