find a minimum value in an array of floats

If you want to use numpy, you must define darr to be a numpy array, not a list:

import numpy as np
darr = np.array([1, 3.14159, 1e100, -2.71828])
print(darr.min())

darr.argmin() will give you the index corresponding to the minimum.

The reason you were getting an error is because argmin is a method understood by numpy arrays, but not by Python lists.

Python has a min() built-in function:

>>> darr = [1, 3.14159, 1e100, -2.71828]
>>> min(darr)
-2.71828