TypeError: "'numpy.float64' object is not iterable" using python 3.x possibly os module issue?

I am running into seemingly simple issue, but I am still scratching my head, not sure why it isn't working. If you could please provide your feedback, it is greatly appreciated!

What I am trying to do is that I have txt file that has x and y look like the following (x and y are tab separated):

x        y
1500   1
2000   0.5
2500   2
3000   6

In my code I determine my precursor and products to be within a certain x range. Then I want to determine the fraction of my precursor.

The following is my code

import numpy as np
import os #reading files using os module

myfiles = sorted(os.listdir('input_102417apo'))

my_ratio=[]

for file in myfiles:
    with open('input_102417apo/'+file, 'r') as f:  #determining x, y in my txt files
        data = np.loadtxt(f,delimiter='\t') 
        data_filtered_both = data[data[:,1] != 0.000]
        x_array=(data_filtered_both[:,0])
        y_array=(data_filtered_both[:,1])
        y_norm=(y_array/np.max(y_array))
        x_and_y = []
        row = np.array([list (i) for i in zip(x_array,y_norm)])
        for x, y in row:
            if y>0:       
                x_and_y.append((x,y))



    precursor_x=[]
    precursor_y=[]
    for x,y in (x_and_y):
        if x>2260 and x<2280:
            precursor_x.append(x)
            precursor_y.append(y)

    precursor_y_sum=np.sum(precursor_y)


    product6_x=[]
    product6_y=[]
    for x,y in (x_and_y):
        if x>1685 and x<1722:
            product6_x.append(x)
            product6_y.append(y)

    product6_y_sum=np.sum(product6_y)


    product5_x=[]
    product5_y=[]    
    for x,y in (x_and_y):
        if x>2035 and x<2080:
            product5_x.append(x)
            product5_y.append(y)    

    product5_y_sum=np.sum(product5_y)


    my_ratio.extend((precursor_y_sum)/(precursor_y_sum+monomer6_y_sum+ monomer5_y_sum))


    with open ('output/'+file, 'w') as f:
        f.write('{0:f}\n'.format(my_ratio))

I am batch processing many files that is organized by a order (number) so I want to have one list that shows a fraction of my precursor from all of my files.

That is why I created my_ratio.

But I am running into the following error message:

TypeError: 'numpy.float64' object is not iterable

I am not quite sure what causes it to be not iterable and how I could fix it. Thanks!