Lazily load pygments styles

[isidentical]

We currently try to retrieve all pygments styles at once, but this operation is very slow due to the import of pkg_resources on the pygments side.
https://github.com/httpie/httpie/blob/cfcd7413d1afbabc5ab3c88a892851335be4944a/httpie/output/formatters/colors.py#L31

We should load these styles lazily when a user specifies --style explicitly.

[isidentical]

Command: hyperfine 'http --version'

	normal	lazy loading	factor
Environment 1	238.2 ms	185.4 ms	1.30X (30%)
Environment 2	383.3 ms	240.4 ms	1.58X (58%)

Since the actual load we are removing is pkg_resources import, the speed-up factor is very dependant on how complex the current python environment you are within. The Environment 1 is simply a fresh python docker image with only httpie installed. The Environment 2 is my local environment with over 300+ python packages.

[isidentical]

(I'll send a patch after #1200)

[jkbrzt]

Nice!

Could we do some quick lookup even if the user specifies --style? Many users probably have --style in their config file.

The full list is probably only needed for --help output. But also even then we only need the names.

[isidentical]

Could we do some quick lookup even if the user specifies --style? Many users probably have --style in their config file.

If users specify --style, they will load the whole pygments (including all of it's plugins). And it will be like the original, so we will error out if the style is not available etc.

The full list is probably only needed for --help output. But also even then we only need the names.

There is actually no cost distinction between the names of the styles and the loading of actual lexers, since most of the time is spent on the pkg_resources import. With this patch, we will only load the pygments on the following 3 occasions:

• When you pass a valid --style (to verify it exists)
• When you pass an invalid --style (to print all the choices)
• To format the help message when run with --help (this is the trickiest, since --help needs to be formatted lazily but there is no easy way to do so).

[jkbrzt]

When you pass a valid --style (to verify it exists)

Couldn’t we use a different method for checking if it exists (e.g. checking if a module exists first, and only then loading the styles if not)? If I use a custom --style (via config, for example), I won’t be able to benefit from this optimization.

[isidentical]

Couldn’t we use a different method for checking if it exists (e.g. checking if a module exists first, and only then loading the styles if not)?

We could introduce layers (e.g check if this is a built-in httpie style > check if this is a built-in pygments style > check if this is coming from a pygments plugin), but I think that would be a bit complicated.

Another possibility is asking pygments maintainers whether they would accept a patch that migrates from pkg_resources to importlib_metadata (a much much faster version for iterating over entry points), if the use case where a --style is also important to us.