Module rcssmin

source code

CSS Minifier.

The minifier is based on the semantics of the YUI compressor, which itself is based on the rule list by Isaac Schlueter.

This module is a re-implementation aiming for speed instead of maximum compression, so it can be used at runtime (rather than during a preprocessing step). RCSSmin does syntactical compression only (removing spaces, comments and possibly semicolons). It does not provide semantic compression (like removing empty blocks, collapsing redundant properties etc). It does, however, support various CSS hacks (by keeping them working as intended).

Here's a feature list:

• Strings are kept, except that escaped newlines are stripped
• Space/Comments before the very end or before various characters are stripped: :{});=>],! (The colon (:) is a special case, a single space is kept if it's outside a ruleset.)
• Space/Comments at the very beginning or after various characters are stripped: {}(=:>[,!
• Optional space after unicode escapes is kept, resp. replaced by a simple space
• whitespaces inside url() definitions are stripped
• Comments starting with an exclamation mark (!) can be kept optionally.
• All other comments and/or whitespace characters are replaced by a single space.
• Multiple consecutive semicolons are reduced to one
• The last semicolon within a ruleset is stripped
• CSS Hacks supported:
  • IE7 hack (>/**/)
  • Mac-IE5 hack (/*\*/.../**/)
  • The boxmodelhack is supported naturally because it relies on valid CSS2 strings
  • Between :first-line and the following comma or curly brace a space is inserted. (apparently it's needed for IE6)
  • Same for :first-letter

rcssmin.c is a reimplementation of rcssmin.py in C and improves runtime up to factor 100 or so (depending on the input). docs/BENCHMARKS in the source distribution contains the details.

Both python 2 (>= 2.4) and python 3 are supported.