How do I use method overloading in Python

Question

I am trying to implement method overloading in Python    class A      def stackoverflow self               print  first method      def stackoverflow self  i           print  second method   i  ob A   ob stackoverflow 2    but the output is second method 2  similarly   class A      def stackoverflow self               print  first method      def stackoverflow self  i           print  second method   i  ob A   ob stackoverflow     gives  Traceback  most recent call last     File  my py   line 9  in  lt module gt      ob stackoverflow   TypeError  stackoverflow   takes exactly 2 arguments  1 given    How do I make this work

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I write my answer in Python 3 2 1   def overload  functions       return lambda  args    kwargs  functions len args    args    kwargs    How it works    overload takes any amount of callables and stores them in tuple functions  then returns lambda  The lambda takes any amount of arguments   then returns result of calling function stored in functions number of unnamed args passed  called with arguments  passed to the lambda    Usage   class A      stackoverflow overload                               None              there is always a self argument  so this should never get called         lambda self  print  First method                   lambda self  i  print  Second method   i

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In Python  you d do this with a default argument   class A       def stackoverflow self  i None               if i    None              print  first method          else              print  second method  i

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Python 3 x includes standard typing library which allows for method overloading with the use of  overload decorator  Unfortunately  this is to make the code more readable  as the  overload decorated methods will need to be followed by a non-decorated method that handles different arguments   More can be found here here but for your example   from typing import overload from typing import Any  Optional class A object        overload     def stackoverflow self  - gt  None              print  first method        overload     def stackoverflow self  i  Any  - gt  None          print  second method   i      def stackoverflow self  i  Optional Any    None  - gt  None          if not i              print  first method           else              print  second method   i   ob A   ob stackoverflow 2

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I just came across overloading py  function overloading for Python 3  for anybody who may be interested  From the linked repository s README file   overloading is a module that provides function dispatching based on the types and number of runtime arguments  When an overloaded function is invoked  the dispatcher compares the supplied arguments to available function signatures and calls the implementation that provides the most accurate match  Features Function validation upon registration and detailed resolution rules guarantee a unique  well-defined outcome at runtime  Implements function resolution caching for great performance  Supports optional parameters  default values  in function signatures  Evaluates both positional and keyword arguments when resolving the best match  Supports fallback functions and execution of shared code  Supports argument polymorphism  Supports classes and inheritance  including classmethods and staticmethods

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Python does not support method overloading like Java or C    We may overload the methods  but we can only use the latest defined method    First sum method    Takes two argument and print their sum def sum a  b       s   a   b     print s     Second sum method   Takes three argument and print their sum def sum a  b  c       s   a   b   c     print s     Uncommenting the below line shows an error   sum 4  5     This line will call the second sum method sum 4  5  5   We need to provide optional arguments or  args in order to provide a different number of arguments on calling  Courtesy Python   Method Overloading

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You can also use pythonlangutil   from pythonlangutil overload import Overload  signature  class A       Overload      signature       def stackoverflow self               print  first method        stackoverflow overload      signature  int       def stackoverflow self  i           print  second method   i

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In Python  overloading is not an applied concept  However  if you are trying to create a case where  for instance  you want one initializer to be performed if passed an argument of type foo and another initializer for an argument of type bar then  since everything in Python is handled as object  you can check the name of the passed object s class type and write conditional handling based on that   class A     def   init   self  arg          Get the Argument s class type as a String       argClass   arg   class     name          if argClass     foo            print  Arg is of type  foo                      elif argClass     bar            print  Arg is of type  bar                      else          print  Arg is of a different type                 This concept can be applied to multiple different scenarios through different methods as needed

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I write my answer in Python 2 7   In Python  method overloading is not possible  if you really want access the same function with different features  I suggest you to go for method overriding   class Base      Base class        def add self a b           s a b         print s         def add self a b c           self a a         self b b         self c c          sum  a b c         print sum  class Derived Base     Derived class     def add self a b     overriding method         sum a b         print sum    add fun 1 Base    instance creation for Base class add fun 2 Derived   instance creation for Derived class  add fun 1 add 4 2 5    function with 3 arguments add fun 2 add 4 2      function with 2 arguments

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It s method overloading  not method overriding  And in Python  you do it all in one function  class A       def stackoverflow self  i  some default value            print  only method   ob A   ob stackoverflow 2  ob stackoverflow    You can t have two methods with the same name in Python -- and you don t need to  See the Default Argument Values section of the Python tutorial  See  quot Least Astonishment quot  and the Mutable Default Argument for a common mistake to avoid  See PEP 443 for information about the new single dispatch generic functions in Python 3 4

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You can t  never need to and don t really want to   In Python  everything is an object  Classes are things  so they are objects  So are methods   There is an object called A which is a class  It has an attribute called stackoverflow  It can only have one such attribute   When you write def stackoverflow            what happens is that you create an object which is the method  and assign it to the stackoverflow attribute of A  If you write two definitions  the second one replaces the first  the same way that assignment always behaves   You furthermore do not want to write code that does the wilder of the sorts of things that overloading is sometimes used for  That s not how the language works   Instead of trying to define a separate function for each type of thing you could be given  which makes little sense since you don t specify types for function parameters anyway   stop worrying about what things are and start thinking about what they can do   You not only can t write a separate one to handle a tuple vs  a list  but also don t want or need to   All you do is take advantage of the fact that they are both  for example  iterable  i e  you can write for element in container     The fact that they aren t directly related by inheritance is irrelevant

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I think the word you re looking for is  quot overloading quot   There isn t any method overloading in Python  You can however use default arguments  as follows  def stackoverflow self  i None       if i    None          print  second method   i     else          print  first method   When you pass it an argument  it will follow the logic of the first condition and execute the first print statement  When you pass it no arguments  it will go into the else condition and execute the second print statement

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In the MathMethod py file  from multipledispatch import dispatch  dispatch int  int  def Add a  b      return a   b   dispatch int  int  int    def Add a  b  c      return a   b   c   dispatch int  int  int  int      def Add a  b  c  d      return a   b   c   d  In the Main py file import MathMethod as MM  print MM Add 200  1000  1000  200    We can overload the method by using multipledispatch

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Python added the  overload decorator with PEP-3124 to provide syntactic sugar for overloading via type inspection - instead of just working with overwriting  Code example on overloading via  overload from PEP-3124 from overloading import overload from collections import Iterable  def flatten ob        quot  quot  quot Flatten an object to its component iterables quot  quot  quot      yield ob   overload def flatten ob  Iterable       for o in ob          for ob in flatten o               yield ob   overload def flatten ob  basestring       yield ob  is transformed by the  overload-decorator to  def flatten ob       if isinstance ob  basestring  or not isinstance ob  Iterable           yield ob     else          for o in ob              for ob in flatten o                   yield ob

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In Python  you don t do things that way  When people do that in languages like Java  they generally want a default value  if they don t  they generally want a method with a different name   So  in Python  you can have default values   class A object      Remember the   object   bit when working in Python 2 x      def stackoverflow self  i None           if i is None              print  first form          else              print  second form    As you can see  you can use this to trigger separate behaviour rather than merely having a default value    gt  gt  gt  ob   A    gt  gt  gt  ob stackoverflow   first form  gt  gt  gt  ob stackoverflow 2  second form

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While agf was right with the answer in the past  now with PEP-3124 we got our syntactic sugar  See typing documentation for details on the  overload decorator  but note that this is really just syntactic sugar and IMHO this is all people have been arguing about ever since  Personally  I agree that having multiple functions with different signatures makes it more readable then having a single function with 20  arguments all set to a default value  None most of the time  and then having to fiddle around using endless if  elif  else chains to find out what the caller actually wants our function to do with the provided set of arguments  This was long overdue following the Python Zen   Beautiful is better than ugly   and arguably also  Simple is better than complex   Straight from the official Python documentation linked above  from typing import overload  overload def process response  None  - gt  None           overload def process response  int  - gt  Tuple int  str            overload def process response  bytes  - gt  str          def process response        lt actual implementation gt

[python] How do I use method overloading in Python?

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