0 Positional arguements but one given but why

Question

On python 3.3 using Ipython

class Gear:
    def __init__(self,chainring,cog):
        self.chainring = chainring
        self.cog  = cog
    def ratio () :
        ratio = self.chainring/self.cog
        return ratio


mygear = Gear(52,11)
mygear.ratio()

Error

TypeError: ratio() takes 0 positional arguments but 1 was given

Related question: [Why accessing to class variable from within the class needs “self.” in Python?](http://stackoverflow.com/q/13652006/510937) — Bakuriu, Jan 23 '14 at 13:15

score 7 · Accepted Answer · answered Jan 23 '14 at 13:13

When you say

mygear.ratio()

python will internally invoke the function like this

ratio(mygear)

But as per the definition of that function,

def ratio () :

it doesn't accept any input parameters. Change it to accept the current object, like this

def ratio(self):

score 2 · Answer 2 · answered Jan 23 '14 at 13:13

2

def ratio(self):

You need to put self inside the methods

answered Jan 23 '14 at 13:13

petabyte

1,487
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score 2 · Answer 3 · answered Jan 23 '14 at 13:13

2

All instance methods in Python need to take the self argument.

def ratio(self):

answered Jan 23 '14 at 13:13

Daniel Roseman

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0 Positional arguements but one given but why

3 Answers3