Support changing gmt defaults

[seisman]

Description of the desired feature

Changing gmt defaults in GMT CLI:

1. gmt set PAR1=value1 PAR2=value2
2. gmt plot ... --PAR1=value1 --PAR2=value2

In pygmt, these two should be:

1. gmt.set(PAR1=value1, PAR2=value2)
2. gmt.plot(projection="xxx", region="xxx", PAR1=value1, PAR2=value2)

Another way is using dict, e.g. gmt.conf['PAR1']=value1, which seems more pythonic. But we need call gmt set for each assignment. I'm not sure if it's technically possible.

[leouieda]

Using the dictionary syntax is doable through __getitem__ but it's probably not worth the added complexity.

I like the set function but not really the upper case arguments to other functions. A better way to have temporary settings would be through a context manger:

with pygmt.set(bla=something):
    pygmt.surface(...)

That would make the documentation of other methods easier because they don't take GMT level configuration parameters. These are all handled by set and can be set globally or temporally.

[liamtoney]

It seems to me like the most common use case of gmt set is for global changes at the beginning of a script. Wouldn't using a context manager cause the whole script to be indented?

In spite of the apparent added complexity (I'm sorry to comment on something I know so little about here) I feel that a dictionary of values would certainly be most suitable. As @seisman has written it above, this would be essentially analogous to what matplotlib does with matplotlib.rcParams, e.g.

import matplotlib as mpl
mpl.rcParams['lines.linewidth'] = 2
mpl.rcParams['lines.color'] = 'r'

If we were using this dictionary framework I think it would be less weird to use upper case arguments, since they're constants anyhow. This would make it simpler since we wouldn't have to come up with new, lower-case names for all of the default params, and folks could cross over from classic GMT more easily.

[leouieda]

Wouldn't using a context manager cause the whole script to be indented?

Yep, that would be terrible. The way the new matplotlib styling works is that you can set a style globally or use a context manager to temporarily change the style. We can tell whether the context manager is called inside a with block. So you could:

pygmt.set(PARAMETER=value)  # Global

# Locally set a value that will revert back to the default
with pygmt.set(PROJ_ELLIPSOID=value):
    ...

pygmt.whatever(...)

What do you think?

If we were using this dictionary framework I think it would be less weird to use upper case arguments

That's a good point. But the set function would be using **kwargs anyway, which is basically a dict.

This would make it simpler since we wouldn't have to come up with new, lower-case names for all of the default params

That was never my intension (sorry for not making it clear). We should keep the same parameter names with upper case letters.

folks could cross over from classic GMT more easily

If that's the case, then calling pygmt.set(...) at the beginning of the script is probably closer to what people do in bash scripts, right?

[liamtoney]

Okay, thanks for the clarification. I think the code block in your comment above represents an ideal implementation since users have both temp and global options.