No nested differentiation:<p><pre><code> >>> import tangent
>>> import numpy as np
>>> tangent.grad(tangent.grad(np.sin))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python3.6/site-packages/tangent/grad_util.py", line 178, in grad
node, namespace = grad_tree(func, wrt, motion, mode, preserve_result, verbose)
File "/usr/local/lib/python3.6/site-packages/tangent/grad_util.py", line 97, in grad_tree
namespace.update(six.get_function_globals(func))
AttributeError: 'numpy.ufunc' object has no attribute '__globals__'</code></pre>