import numpy as np
# argmin returns the first encountered index having the minimum
d = np.array([3,2,1,3,2,1,3]
np.argmin(d)
# why?
# take a look at the help of argmin() ' "Notes" section
help(np.argmin)
#  Notes
#   -----
#   In case of multiple occurrences of the minimum values, the indices
#   corresponding to the first occurrence are returned.

np.where(d == d.min()) # will work