Jupyter magic to handle notebook exceptions

Question

I have a few long-running experiments in my Jupyter Notebooks. Because I don\'t know when they will finish, I add an email function to the last cell of the notebook, so I au

Answer 1

Why exec is not always the solution

It's some years later and I had a similar issue trying to handle errors with Jupyter magics. However, I needed variables to persist in the actual Jupyter notebook.

%%try_except print
a = 12
raise ValueError('test')

In this example, I want the error to print (but could be anything such as e-mail as in the opening post), but also a == 12 to be true in the next cell. For that reason, the method exec suggested does not work when you define the magic in a different file. The solution I found is to use the IPython functionalities.

How you can solve it

from IPython.core.magic import line_magic, cell_magic, line_cell_magic, Magics, magics_class


@magics_class
class CustomMagics(Magics):
    @cell_magic
    def try_except(self, line, cell):
        """ This magic wraps a cell in try_except functionality """  
        try:
            self.shell.ex(cell)  # This executes the cell in the current namespace
        except Exception as e:
            if ip.ev(f'callable({how})'):  # check we have a callable handler
                self.shell.user_ns['error'] = e  # add error to namespace
                ip.ev(f'{how}(error)')  # call the handler with the error
            else:
                raise e


# Register
from IPython import get_ipython
ip = get_ipython()
ip.register_magics(CustomMagics)