def handle_exception(stacktrace):
    send_mail_to_myself(stacktrace)


%%in_case_of_notebook_exception handle_exception # <--- this is what I'm looking for

from IPython.core.magic import register_cell_magic

@register_cell_magic
def handle(line, cell):
    try:
        exec(cell)
    except Exception as e:
        send_mail_to_myself(e)
        # Reraise to have the full traceback in the notebook
        raise

%%handle

some_code()
raise ValueError('this exception will be caught by the magic command')

from IPython.core.ultratb import AutoFormattedTB

# initialize the formatter for making the tracebacks into strings
itb = AutoFormattedTB(mode = 'Plain', tb_offset = 1)

# this function will be called on exceptions in any cell
def custom_exc(shell, etype, evalue, tb, tb_offset=None):

    # still show the error within the notebook, don't just swallow it
    shell.showtraceback((etype, evalue, tb), tb_offset=tb_offset)

    # grab the traceback and make it into a list of strings
    stb = itb.structured_traceback(etype, evalue, tb)
    sstb = itb.stb2text(stb)

    print (sstb) # <--- this is the variable with the traceback string
    print ("sending mail")
    send_mail_to_myself(sstb)

# this registers a custom exception handler for the whole current notebook
get_ipython().set_custom_exc((Exception,), custom_exc)