IPython Events
Extension code can register callbacks functions which will be called on specific events within the IPython code. You can see the current list of available callbacks, and the parameters that will be passed with each, in the callback prototype functions defined in :mod:`IPython.core.events`.
To register callbacks, use :meth:`IPython.core.events.EventManager.register`. For example:
class VarWatcher(object):
def __init__(self, ip):
self.shell = ip
self.last_x = None
def pre_execute(self):
self.last_x = self.shell.user_ns.get('x', None)
def pre_run_cell(self, info):
print('info.raw_cell =', info.raw_cell)
print('info.store_history =', info.store_history)
print('info.silent =', info.silent)
print('info.shell_futures =', info.shell_futures)
print('info.cell_id =', info.cell_id)
print(dir(info))
def post_execute(self):
if self.shell.user_ns.get('x', None) != self.last_x:
print("x changed!")
def post_run_cell(self, result):
print('result.execution_count = ', result.execution_count)
print('result.error_before_exec = ', result.error_before_exec)
print('result.error_in_exec = ', result.error_in_exec)
print('result.info = ', result.info)
print('result.result = ', result.result)
def load_ipython_extension(ip):
vw = VarWatcher(ip)
ip.events.register('pre_execute', vw.pre_execute)
ip.events.register('pre_run_cell', vw.pre_run_cell)
ip.events.register('post_execute', vw.post_execute)
ip.events.register('post_run_cell', vw.post_run_cell)
Events
These are the events IPython will emit. Callbacks will be passed no arguments, unless otherwise specified.
shell_initialized
def shell_initialized(ipython): ...
This event is triggered only once, at the end of setting up IPython. Extensions registered to load by default as part of configuration can use this to execute code to finalize setup. Callbacks will be passed the InteractiveShell instance.
pre_run_cell
pre_run_cell fires prior to interactive execution (e.g. a cell in a notebook). It can be used to note the state prior to execution, and keep track of changes. An object containing information used for the code execution is provided as an argument.
pre_execute
pre_execute is like pre_run_cell, but is triggered prior to any execution. Sometimes code can be executed by libraries, etc. which skipping the history/display mechanisms, in which cases pre_run_cell will not fire.
post_run_cell
post_run_cell runs after interactive execution (e.g. a cell in a notebook). It can be used to cleanup or notify or perform operations on any side effects produced during execution. For instance, the inline matplotlib backend uses this event to display any figures created but not explicitly displayed during the course of the cell. The object which will be returned as the execution result is provided as an argument.
post_execute
The same as pre_execute, post_execute is like post_run_cell, but fires for all executions, not just interactive ones.