Embedding · Quickstart

This guide covers driving lessish from Python. It assumes you already know Less — if you don't, lesscss.org is the reference. lessish compiles the same language less.js does.

Lessish is the only top-level class you need. Instantiate it once and call compile.

from lessish import Lessish

ls = Lessish()
css = ls.compile('@c: red; .a { color: @c; }')
# => '.a {\n  color: red;\n}\n'

compile takes a string of Less source and returns a string of CSS. That's the whole contract for the common case.

One instance, many compiles

A Lessish instance is cheap and reusable. Per-compile state is built fresh inside each call and never stored on the instance, so a single instance is safe to reuse — and even to share across threads.

from lessish import Lessish

ls = Lessish()
a = ls.compile('.a { width: 1px + 1px; }')
b = ls.compile('.b { color: #fff; }')
# => '.b {\n  color: #fff;\n}\n'
assert a == '.a {\n  width: 2px;\n}\n'

Baking in options

The constructor stores defaults that every compile call inherits; per-call keyword arguments override them. Option names mirror less.js, snake-cased.

from lessish import Lessish

ls = Lessish(compress=True)
minified = ls.compile('.a { color: red; }')
# => '.a{color:red}'

# A per-call override wins over the baked-in default.
pretty = ls.compile('.a { color: red; }', compress=False)
# => '.a {\n  color: red;\n}\n'

The full option set — paths, math, global_vars, source_map, file_io, and the rest — is in 02-options.md.

Compiling a file

compile takes source text, not a path, so read the file yourself and pass filename so error messages and @import resolution have a base path.

# docs: skip
from lessish import Lessish

ls = Lessish()
css = ls.compile(
    open('styles.less', encoding='utf-8').read(),
    filename='styles.less',
)

(Marked skip above because it touches the filesystem; the behaviour is exercised by the CLI in ../cli.md.)

A note on the security warning

file_io defaults to the secure 'jail', so the default is silent. If you opt into the less.js-compatible file_io='allow' (Less source can read any file the process can), lessish emits a LessishSecurityWarning on every such compile — informational, never written to the returned CSS. When the input is trusted and you genuinely want 'allow', silence the warning explicitly:

import warnings
from lessish import Lessish, LessishSecurityWarning

warnings.filterwarnings('ignore', category=LessishSecurityWarning)
css = Lessish(file_io='allow').compile('.a { color: red; }')
# => '.a {\n  color: red;\n}\n'

For untrusted input, keep the default 'jail' (or use 'deny') rather than reaching for 'allow' — see 02-options.md.

Next: Options →