# Execute Time¶

This extension displays when the last execution of a code cell occurred, and how long it took.

Every executed code cell is extended with a new area, attached at the bottom of the input area, that displays the time at which the user sent the cell to the kernel for execution. When the kernel finishes executing the cell, the area is updated with the duration of the execution. The timing information is stored in the cell metadata, and restored on notebook load.

## Toggling display¶

The timing area can be hidden by double clicking on it, or using the Cell -> Toggle timings -> Selected menu item. The menu item Cell -> Toggle timings -> All hides (shows) all the timing areas in the notebook, if the first cell is currently shown (hidden).

## Options¶

The nbextension offers a few options for how to display and interpret timestamps. Options are stored in the notebook section of the server’s nbconfig, under the key ExecuteTime. The easiest way to configure these is using the jupyter_nbextensions_configurator, which if you got this nbextension in the usual way from jupyter_contrib_nbextensions, should also have been installed.

Alternatively, you can also configure them directly with a few lines of python. For example, to alter the displayed message, use relative timestamps, and set them to update every 5 seconds, we can use the following python snippet:

from notebook.services.config import ConfigManager
ConfigManager().update('notebook', {'ExecuteTime': {
'display_absolute_timestamps': False,
'relative_timing_update_period': 5,
'template': {
'executed': 'started ${start_time}, finished in${duration}',
}
}})


The available options are:

• ExecuteTime.clear_timings_on_clear_output: When cells’ outputs are cleared, also clear their timing data, e.g. when using the Kernel > Restart & Clear Output menu item
• ExecuteTime.clear_timings_on_kernel_restart: Clear all cells’ execution timing data on any kernel restart event
• ExecuteTime.display_absolute_timings: Display absolute timings for the start/end time of execution. Setting this false will result in the display of a relative timestamp like ‘a few seconds ago’ (see the moment.js function fromNow for details). Defaults to true.
• ExecuteTime.display_absolute_format: The format to use when displaying absolute timings (see ExecuteTime.display_absolute_timings, above). See the moment.js function format for details of the template tokens available. Defaults to 'YYYY-MM-DD HH:mm:ss'.
• ExecuteTime.relative_timing_update_period: Seconds to wait between updating the relative timestamps, if using them (see ExecuteTime.display_absolute_timings, above). Defaults to 10.
• ExecuteTime.display_in_utc: Display times in UTC, rather than in the local timezone set by the browser. Defaults to false.
• ExecuteTime.default_kernel_to_utc: For kernel timestamps which do not specify a timezone, assume UTC. Defaults to true.
• ExecuteTime.display_right_aligned: Right-align the text in the timing area under each cell. Defaults to false.
• ExecuteTime.highlight.use: Highlight the displayed execution time on completion of execution. Defaults to true.
• ExecuteTime.highlight.color: Color to use for highlighting the displayed execution time. Defaults to '#00BB00'.
• ExecuteTime.template.executed: Template for the timing message for executed cells. See readme for replacement tokens. Defaults to 'executed in ${duration}, finished${end_time}'.
• ExecuteTime.template.queued: Template for the timing message for queued cells. The template uses an ES2015-like syntax, but replaces only the exact strings ${start_time}, plus (if defined) ${end_time} and ${duration}. Defaults to 'execution queued${start_time}'.

## Limitations¶

### timezones¶

As discussed in ipython-contrib/jupyter_contrib_nbextensions#549, ipython-contrib/jupyter_contrib_nbextensions#904, and jupyter/jupyter_client#143, although they are (now) supposed to, Jupyter kernels don’t always specify a timezone for their timestamps, which can cause problems when the moment.js library assumes the local timezone, rather than UTC, which is what most kernels are actually using. To help to address this, see the options above, which can be used to assume UTC for unzoned timestamps.

### execution queues¶

For a reason I don’t understand, when multiple cells are queued for execution, the kernel doesn’t send a reply immediately after finishing executing each cell. Some replies are delayed, and sent at the same time as later replies, meaning that the output of a cell can be updated with its finished value, before the notebook recieves the kernel execution reply. For the same reason, you can see this in the fact that the star for an executing cell can remain next to two cells at once, if several are queued to execute together. Since this extension uses the times in the kernel message (see internals, below), and these remain correct, the timings displayed are still accurate, but they may get displayed later due to this kernel issue.

## Installation¶

Install the master version of the jupyter_contrib_nbextensions repository as explained in the docs at jupyter-contrib-nbextensions.readthedocs.io.

Then you can use the jupyter_nbextensions_configurator to enable/disable this extension for all notebooks.

## Internals¶

The execution start and end times are stored in the cell metadata as ISO8601 strings, for example:

{
"ExecuteTime": {
"start_time": "2016-02-11T18:51:18.536796",
"end_time": "2016-02-11T18:51:35.806119"
}
}


The times in the timing areas are formatted using the moment.js library (already included as part of Jupyter), but the durations use a custom formatting function, as I (@jcb91) couldn’t find an existing one that I liked.

The event execute.CodeCell is caught in order to create a start time, and add the timing area with its ‘Execution queued at’ message. The extension again uses moment.js for formatting this as an ISO string time.

To determine the execution time, the extension patches the Jupyter class prototype CodeCell.prototype.get_callbacks from notebook/js/codecell.js. This patch then patches the callbacks.shell.reply function returned by the original CodeCell.prototype.get_callbacks, wrapping it in a function which reads the msg.header.date value from the kernel message, to provide the execution end time. This is more accurate than creating a new time, which can be affected by client-side variability. In addition, for accurate timings, the start time is also revised using the msg.metadata.started value supplied in the callback, which can be very different from the time the cell was queued for execution (as a result of other cells already being executed). The kernel reply message times are already ISO8601 strings, so no conversion is necessary, although again, moment.js is used for parsing and diff’ing them.