>>> from math import sqrt >>> sqrt(-1) Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: math domain error >>> from numpy import sqrt >>> sqrt(-1) Warning: invalid value encountered in sqrt nan >>> from cmath import sqrt # complex math functions >>> sqrt(-1) 1j >>> sqrt(4) # cmath functions always return complex... (2+0j) >>> from numpy.lib.scimath import sqrt >>> sqrt(4) 2.0 # real when possible >>> sqrt(-1) 1j # otherwise complex
