Resetting default GMT parameters - pygmt.config

[hemmelig]

Description of the desired feature

The pygmt.config class/context manager allows the user to permanently or temporarily override default GMT config parameters. If a parameter is set permanently (particularly in a notebook), it would be useful to be able to reset back to the default without having to reset the kernel / use pygmt.config as a context manager. Motivated by #482 (comment)

Are you willing to help implement and maintain this feature? Yes

I've been able to override and reset everything myself by terminating and restarting the global session:

from pygmt import session_management

session_management.end()
session_management.begin()

but this is obviously not ideal, and I fear this may have unintended consequences of which I'm ignorant. I see this feature more as something to facilitate figure development in a notebook, but not so much for finalised figure scripts/notebooks, so it's perhaps not a huge issue?

Ideal usage would be something like:

pygmt.config().reset()

I'm still familiarising myself with the inner workings, so I apologise if I've missed/misunderstood something important.

[weiji14]

GMT has a gmtdefaults function that may help with this. However, it might not respect the user's gmt.conf properly (correct me if I'm wrong)? Was actually mentioned in #293 (review) when we wrote the test case, but we just reverted it like so

pygmt/pygmt/tests/test_config.py

Lines 35 to 36 in 0fc2e94

	# Revert to default settings
	config(FONT_ANNOT_PRIMARY="black")

Alternatively, there might be a way to 'store' a global list of all the configurations a user has made and reuse some part of the __exit__ code:

pygmt/pygmt/modules.py

Lines 180 to 186 in 0fc2e94

	def __exit__(self, exc_type, exc_value, traceback):
	# revert to initial values
	arg_str = " ".join(
	["{}={}".format(key, value) for key, value in self.old_defaults.items()]
	)
	with Session() as lib:
	lib.call_module("set", arg_str)

[seisman]

I think things is a little different after we bump to GMT>6.1.

In GMT 6.1, the GMT settings also have a hierarchical level. Each session, figure and subplot all can have its own configurations.

See https://docs.generic-mapping-tools.org/6.1/cookbook/features.html#gmt-modern-mode-hierarchical-levels.

[seisman]

GMT has a gmtdefaults function that may help with this. However, it might not respect the user's gmt.conf properly (correct me if I'm wrong)?

I think you're right. gmtdefaults can only list: (1) the current defaults; (2) the system defaults (either in SI or US units).

Alternatively, there might be a way to 'store' a global list of all the configurations a user has made and reuse some part of the __exit__ code:

Yes, it's possible to have a _global_defaults property which can store the session-level defaults.

So, perhaps we can have pygmt.config().reset(type="user") in which type can be:

• user: can be reset by using the _global_defaults property.
• system_us and system_si: can be reset by using the gmtdefaults module.

Or we can ask an upstream feature request to allow gmtdefaults report the session-level defaults?