How to access a cell of a grid using a 2d array in python?

Question

I'm tryin to bilerp a cell into one value using python for a NetCDF data set. I'm new to python and I can't understand what I'm doing wrong here. I have a 2d array and I give the four points by iterating through the dataset dataArr. I use Lerp method for the calculation. Somehow when I pass the 3 values it seems to consider it as more than 3. What am I doing wrong here? Thanks in adv.

This is the error I get>> self.Lerp((dataArr[i][j]),(dataArr[i+1][j]),fraction) takes exactly 3 arguments (4 given)

def compute(self,varval):      
        vars=self.data.variables
        for var in vars:
            if var==varval:
                ntimes, ny, nx=vars[var].shape #inherit the method above.
        print(ntimes, ny, nx)
        #create the old computational grid.
        computational_grid=np.zeros((ny,nx),dtype=int) 
        fraction=.5 
        newnx,newny =(nx*fraction,ny*fraction)
        new_computational_grid=np.zeros((newny,newnx),dtype=int)
        phy_value_arr=self.get_data(varval)
        t=10 #send this t value with coords
        dataArr=self.data.variables['tos'][t]     
        for i in range(0,(ny-1),1):
            for j in range(0,(nx-1),1):
               a=self.Lerp((dataArr[i][j]),(dataArr[i+1][j]),fraction)
               b=self.Lerp((dataArr[i][j]),(dataArr[i+1][j]),fraction)
               self.tempY.append(self.Lerp(a,b,fraction))
       tempY.reshape(newnx,newny)
       pcolormesh(self.tempY)
       colorbar()

def Lerp( _a, _b, _t) :
      return _a+(_b-_a)*_t

Answer 1

You call Lerp like tihs:

self.Lerp(a,b,fraction)

By definition it will put self as the first argument. Thus you will have four in total. However, you define Lerp as

def Lerp( _a, _b, _t) : #<- this takes only three arguments

I think it should be:

def Lerp(self, _a, _b, _t) : #<- this takes four, and self is first one