def minimum(a_list):

    a_min = a_list[0]    # Warning! List must not be empty!

    for a in a_list:
        if a < a_min:
            a_min = a

    return a_min



print minimum([4.0, 3.0, 5.0])

values = [12, 5]
print minimum(values)

# print minimum([])