import numpy as np
arr = np.full((10,), -1, np.int64)

import numpy as np
data_type = [("value_1", np.int64), ("value_2", np.float64)]
default = (-1, np.nan)
arr = np.full((10,), default, data_type)

default_array = np.array([default], data_type)
new_default = default_array[0]
arr = np.full((10,), new_default, data_type)