Consider switching to argparse for nicer command line handling and help

[manics]

Proposed change

Switch from tornado.options to argparse (or traitlets, though argparse is easier for a small utility like this) for handling command line arguments

Alternative options

Do nothing

Who would use this feature?

Anyone wanting a nice help message. Currently it looks like this

Usage: /opt/conda/envs/test/bin/jupyterhub-idle-culler [OPTIONS]

Options:

  --help                           show this help information

/opt/conda/envs/test/lib/python3.9/site-packages/jupyterhub_idle_culler/__init__.py options:

  --api-page-size                  Number of users to request per page, when
                                   using JupyterHub 2.0's paginated user list
                                   API. Default: user the server-side default
                                   configured page size. (default 0)
  --concurrency                    Limit the number of concurrent requests made
                                   to the Hub.  Deleting a lot of users at the
                                   same time can slow down the Hub, so limit
                                   the number of API requests we have
                                   outstanding at any given time. (default 10)
  --cull-admin-users               Whether admin users should be culled (only
                                   if --cull-users=true). (default True)
  --cull-every                     The interval (in seconds) for checking for
                                   idle servers to cull. (default 0)
  --cull-users                     Cull users in addition to servers.  This is
                                   for use in temporary-user cases such as
                                   tmpnb. (default False)
  --internal-certs-location        The location of generated internal-ssl
                                   certificates (only needed with --ssl-
                                   enabled=true). (default internal-ssl)
  --max-age                        The maximum age (in seconds) of servers that
                                   should be culled even if they are active.
                                   (default 0)
  --remove-named-servers           Remove named servers in addition to stopping
                                   them.  This is useful for a BinderHub that
                                   uses authentication and named servers.
                                   (default False)
  --ssl-enabled                    Whether the Jupyter API endpoint has TLS
                                   enabled. (default False)
  --timeout                        The idle timeout (in seconds). (default 600)
  --url                            The JupyterHub API URL.

/opt/conda/envs/test/lib/python3.9/site-packages/tornado/log.py options:

  --log-file-max-size              max size of log files before rollover
                                   (default 100000000)
  --log-file-num-backups           number of log files to keep (default 10)
  --log-file-prefix=PATH           Path prefix for log files. Note that if you
                                   are running multiple tornado processes,
                                   log_file_prefix must be different for each
                                   of them (e.g. include the port number)
  --log-rotate-interval            The interval value of timed rotating
                                   (default 1)
  --log-rotate-mode                The mode of rotating files(time or size)
                                   (default size)
  --log-rotate-when                specify the type of TimedRotatingFileHandler
                                   interval other options:('S', 'M', 'H', 'D',
                                   'W0'-'W6') (default midnight)
  --log-to-stderr                  Send log output to stderr (colorized if
                                   possible). By default use stderr if
                                   --log_file_prefix is not set and no other
                                   logging is configured.
  --logging=debug|info|warning|error|none 
                                   Set the Python log level. If 'none', tornado
                                   won't touch the logging configuration.
                                   (default info)

Problems include:

• The help message is interrupted by a path to a source file e.g. /opt/conda/envs/test/lib/python3.9/site-packages/jupyterhub_idle_culler/__init__.py
• It's not clear to a new user how to use boolean options. E.g. can they be used as flags (--cull-users instead of --cull-users=true), what values can they take (is it just true/false, or are other values like 0/1 accepted)
• It's not immediately obvious that = is required (--url http://localhost/ is invalid)
• /opt/conda/envs/test/lib/python3.9/site-packages/tornado/log.py options are arguably irrelevant

(Optional): Suggest a solution

Use argparse instead. Boolean options would be implemented as choices=["true","false"] instead of a flag for compatibility.

Get rid of the logging options? This would be a breaking change though.

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[consideRatio]

I'm 👍 for a switch to argparse!

[manics]

One factor when choosing between argparse and traitlets is how we want to handle extensions and their configuration.

• How configurable should the culler be? #9
• Support custom culling logic through hooks (like Spawner's pre_spawn_hook etc) #25