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A Python less compiler

Project Description

The lessc Python package compiles content in LESS syntax into CSS by first preprocessing it and then invoking the nodejs lessc program to actually compile it. The preprocessing resolves imports which allows the LESS content to come from anywhere, including the filesystem, zipped EGG files, databases, etc. This solves one of the greatest limitations of the nodejs lessc program which requires all of the LESS dependencies to be actual files and imports to be non-absolute.

It is possible, but quite improbable, that this package turns into a pure-Python implementation of a LESS compiler.

For more information on LESS, please see


$ npm install lessc
$ export PATH="`pwd`/node_modules/.bin:$PATH"
$ pip install lessc


import lessc

# compile a less asset in the "mypackage" python module:
css = lessc.compile_asset('mypackage:path/to/style.less')

# compile a less file on the filesystem
css = lessc.compile_file('../path/to/style.less')

# compile a less file-like object
# (if there are any relative imports, specifying `base` is necessary)
css = lessc.compile_file(open('../path/to/style.less'))

# compile a less string
# (if there are any relative imports, specifying `base` is necessary)

less = '''
  @import "mypackage:path/to/style.less";
  // ...other less statements...

css = lessc.compile(less)

For more import resolution control, you can specify a custom URI resolver (which resolves a relative URI to an absolute URI) and a custom URI loader (which loads an absolute URI), using the resolver and loader keywords to any compile* function:

import lessc

def resolver(uri, base=None):
  Returns the absolute URI given a base URI and a potentially
  absolute or relative URI. Note that `base` may be ``None`` when
  the initial URI is being resolved (depending on the Compiler
  # calculate the absolute URI...
  return absolute_uri

def loader(uri):
  Returns a file-like object that will return the content of
  the specified URI.
  # fetch the object defined by `uri`
  return file_like_object

css = lessc.compile_asset(uri, resolver=resolver, loader=loader)

Or you can create a custom compiler and set it as the default compiler:

import lessc

compiler = lessc.Compiler(resolver=my_custom_resolver, loader=my_custom_loader)

# this will now use `my_custom_resolver` and `my_custom_loader`
# to compile asset `uri`
css = lessc.compile_asset(uri)


Currently, there exist the following restrictions in what kind of LESS syntax is used:

  • Recursive imports are not supported and will be silently ignored.

  • Only the following import keywords are explicitly supported:

    • less
    • css
    • once
    • optional

    The keywords reference, inline, and multiple are NOT supported. Any other keywords may or may not be supported (since only the above keywords were documented as of this writing, 2015/06/26).

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