import numpy as np

A = np.array([2, 1, 3, 8, 5, 4, 0])

x = 3.4

i_match = np.argmin(np.abs(x - A))
a_match = A[i_match]

print('x =', x)
print('i_match =', i_match)
print('a_match =', a_match)