Python interpreter error x takes no arguments 1 given

Question

I m writing a small piece of python as a homework assignment  and I m not getting it to run  I don t have that much Python-experience  but I know quite a lot of Java   I m trying to implement a Particle Swarm Optimization algorithm  and here s what I have    class Particle           def   init   self domain ID           self ID   ID         self gbest   None         self velocity              self current              self pbest              for x in range len domain                self current append random randint domain x  0  domain x  1                 self velocity append random randint domain x  0  domain x  1                 self pbestx   self current                def updateVelocity        for x in range 0 len self velocity            self velocity x    2 random random    self pbestx x -self current x     2   random random    self gbest x -self current x          def updatePosition                for x in range 0 len self current                self current x    self current x    self velocity x           def updatePbest            if costf self current   lt  costf self best               self best   self current              def psoOptimize domain costf noOfParticles 20  noOfRuns 30           particles              for i in range noOfParticles                   particle   Particle domain i                  particles append particle               for i in range noOfRuns               Globalgbest                  cost   9999999999999999999         for i in particles              if costf i pbest   lt  cost                  cost   costf i pbest              Globalgbest   i pbest             for particle in particles                  particle updateVelocity                   particle updatePosition                   particle updatePbest costf                  particle gbest   Globalgbest               return determineGbest particles costf    Now  I see no reason why this shouldn t work   However  when I run it  I get this error    TypeError  updateVelocity   takes no arguments  1 given    I don t understand  I m not giving it any arguments   Thanks for the help   Linus

User · Answer

I have been puzzled a lot with this problem, since I am relively new in Python. I cannot apply the solution to the code given by the questioned, since it's not self executable. So I bring a very simple code:

from turtle import *

ts = Screen(); tu = Turtle()

def move(x,y):
  print "move()"
  tu.goto(100,100)

ts.listen();
ts.onclick(move)

done()

As you can see, the solution consists in using two (dummy) arguments, even if they are not used either by the function itself or in calling it! It sounds crazy, but I believe there must be a reason for it (hidden from the novice!).

I have tried a lot of other ways ('self' included). It's the only one that works (for me, at least).

User · Answer

Make sure  that all of your class methods  updateVelocity  updatePosition       take at least one positional argument  which is canonically named self and refers to the current instance of the class   When you call particle updateVelocity    the called method implicitly gets an argument  the instance  here particle as first parameter

User · Answer

Your updateVelocity   method is missing the explicit self parameter in its definition    Should be something like this   def updateVelocity self           for x in range 0 len self velocity            self velocity x    2 random random    self pbestx x -self current x     2               random random    self gbest x -self current x     Your other methods  except for   init    have the same problem

User · Answer

Python implicitly passes the object to method calls  but you need to explicitly declare the parameter for it  This is customarily named self   def updateVelocity self

[python] Python interpreter error, x takes no arguments (1 given)

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