class method generates TypeError got multiple values for keyword argument

Question

If I define a class method with a keyword argument thus   class foo object     def foodo thing None  thong  not underwear        print thing if thing else  nothing       print  a thong is  thong   calling the method generates a TypeError   myfoo   foo   myfoo foodo thing  something        TypeError  foodo   got multiple values for keyword argument  thing    What s going on

User · Answer

This might be obvious  but it might help someone who has never seen it before   This also happens for regular functions if you mistakenly assign a parameter by position and explicitly by name    gt  gt  gt  def foodo thing None  thong  not underwear            print thing if thing else  nothing          print  a thong is  thong      gt  gt  gt  foodo  something   thing  everything   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  foodo   got multiple values for keyword argument  thing

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The problem is that the first argument passed to class methods in python is always a copy of the class instance on which the method is called  typically labelled self  If the class is declared thus   class foo object     def foodo self  thing None  thong  not underwear        print thing if thing else  nothing       print  a thong is  thong   it behaves as expected    Explanation   Without self as the first parameter  when myfoo foodo thing  something   is executed  the foodo method is called with arguments  myfoo  thing  something    The instance myfoo is then assigned to thing  since thing is the first declared parameter   but python also attempts to assign  something  to thing  hence the Exception   To demonstrate  try running this with the original code   myfoo foodo  something   print print myfoo   You ll output like    lt   main   foo object at 0x321c290 gt  a thong is something   lt   main   foo object at 0x321c290 gt    You can see that  thing  has been assigned a reference to the instance  myfoo  of the class  foo   This section of the docs explains how function arguments work a bit more

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Also this can happen in Django if you are using jquery ajax to url that reverses to a function that doesn t contain  request  parameter    ajax     url      url to myfunc            def myfunc foo  bar

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Thanks for the instructive posts  I d just like to keep a note that if you re getting  TypeError  foodo   got multiple values for keyword argument  thing    it may also be that you re mistakenly passing the  self  as a parameter when calling the function  probably because you copied the line from the class declaration - it s a common error when one s in a hurry

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I want to add one more answer       It  happens when you try to pass positional parameter with wrong   position order along with keyword argument in calling function    there is difference between parameter and argument you can read in detail about here Arguments and Parameter in python  def hello a b 1   args      print a  b   args    hello 1  2  3  4 a 12    since we have three parameters    a is positional parameter  b 1 is keyword and default parameter    args is variable length parameter   so we first assign a as positional parameter   means we have to provide value to positional argument in its position order  here order matter  but we are passing argument 1 at the place of a in calling function and then we are also providing value to a   treating as keyword argument  now a have two values    one is positional value  a 1  second is keyworded value which is a 12  Solution  We have to change hello 1  2  3  4 a 12  to hello 1  2  3  4 12  so now a will get only one positional value which is 1 and b will get value 2 and rest of values will get  args  variable length parameter   additional information  if we want that  args should get 2 3 4 and a  should get 1 and b should get  12   then we can do like this def hello a  args b 1        pass hello 1  2  3  4 b 12   Something more    def hello a  c b 1   kwargs       print b      print c      print a      print kwargs   hello 1 2 1 2 8 9 c 12    output    1   2  1  2  8  9   1    c   12

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This error can also happen if you pass a key word argument for which one of the keys is similar  has same string name  to a positional argument    gt  gt  gt  class Foo            def bar self  bar    kwargs                   print bar        gt  gt  gt  kwgs     bar   Barred    jokes   Another key word argument    gt  gt  gt  myfoo   Foo    gt  gt  gt  myfoo bar  fire     kwgs  Traceback  most recent call last   File   lt stdin gt    line 1  in  lt module gt  TypeError  bar   got multiple values for argument  bar   gt  gt  gt      fire  has been accepted into the  bar  argument  And yet there is another  bar  argument present in kwargs   You would have to remove the keyword argument from the kwargs before passing it to the method

User · Answer

just add  staticmethod  decorator to function and problem is fixed  class foo object        staticmethod     def foodo thing None  thong  not underwear            print thing if thing else  nothing           print  a thong is  thong

[python] class method generates "TypeError: ... got multiple values for keyword argument ..."

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