Search for the line number corresponding to a value

[Lali]

Hello,

I have a.csv file with two columns. I search in one of the columns for a value approximating "K" using the following script:

Re=np.loadtxt('./Re.CSV',delimiter=',').T
def closest(lst, K): 

     lst = np.asarray(lst) 
     idx = (np.abs(lst - K)).argmin() 
     return lst[idx] 

# Driver code 
lst = Re[0]
K=72
print(closest(lst, K))

Now, I would like to have the line number corresponding to the approximate value of K, how could I get it back? Do you have any idea?
Thank you,