Get the the closest higher number from a text file

I have a text file. inside there is text like that (no header):

1,2,5,7

I’m trying to get the the closest number to 3, but higher than 3. the answer would be 5.

with open("myfile.txt", "r") as f:
    lines = f.read()
    num = float("10")
    print(min(filter(lambda x: x > num, lines)))

It doesn’t work, it seems there a problem with the list or strings or array.
When I do it like this it works:

num = 3
li = [1,2,5,7]
print (min(filter(lambda x: x > num,li)))

I tried to write it like this [1,2,5,7] in myfile.txt, it’s not working. f.read() and f.readlines() also not working.

>Solution :

This task screams for numpy

import numpy as np

fin = 'myfile.txt'
num = 2
a = np.loadtxt(fin, delimiter=',')
b = np.sort(a)
c = b[b > num][0]
print(c)