How can I take the square root of -1 using python?

Question

When I take the square root of -1 it gives me an error:

invalid value encountered in sqrt

How do I fix that?

from numpy import sqrt
arr = sqrt(-1)
print(arr)

Answer 1

I just discovered the convenience function numpy.lib.scimath.sqrt explained in the sqrt documentation. I use it as follows:

>>> from numpy.lib.scimath import sqrt as csqrt
>>> csqrt(-1)
1j

Answer 2

To avoid the invalid value warning/error, the argument to numpy's sqrt function must be complex:

In [8]: import numpy as np

In [9]: np.sqrt(-1+0j)
Out[9]: 1j

As @AshwiniChaudhary pointed out in a comment, you could also use the cmath standard library:

In [10]: cmath.sqrt(-1)
Out[10]: 1j

Answer 3

You need to use the sqrt from the cmath module (part of the standard library)

>>> import cmath
>>> cmath.sqrt(-1)
1j