rCSSmin - CSS Minifier

rCSSmin is a CSS minifier written in python.

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 50 or so (depending on the input).

rCSSmin works with both python 2 (starting with python 2.4) and python 3.

Documentation

A generated API documentation is available. But you can just look into the module. It provides a simple function, called cssmin which takes the css as a string and returns the minified css as a string.

The module additionally provides a “streamy” interface:

$ python -mrcssmin <css >minified

It takes two options:

-b Keep bang-comments (Comments starting with an exclamation mark)
-p Use the python implementation (not the C implementation)

Development Status

rCSSmin is stable.

License

rCSSmin is available under the terms and conditions of the “Apache License, Version 2.0.” You’ll find the detailed licensing terms in the root directory of the source distribution package or online at http://www.apache.org/licenses/LICENSE-2.0.

Download

Integrity Check

There are hashes (MD5, SHA1 and SHA256) of the download packages stored in the digests file. In order to check the integrity of the downloaded file, use a tool like md5sum (or sha1sum, sha256sum accordingly), e.g.:

$ md5sum -c rcssmin-1.0.4.digests
rcssmin-1.0.4.tar.bz2: OK
rcssmin-1.0.4.tar.gz: OK
rcssmin-1.0.4.tar.xz: OK
rcssmin-1.0.4.zip: OK

In order to check the integrity of the digest file itself, you can check the PGP signature of that file. The file is signed by André Malo, Key-ID 0x8103A37E:

$ gpg --verify rcssmin-1.0.4.digests
gpg: Signature made Sun Feb 23 21:50:55 2014 CET using DSA key ID 8103A37E
gpg: Good signature from "Andre Malo <nd@apache.org>"
gpg:                 aka "Andr\xe9\x20Malo <nd@perlig.de>"
gpg:                 aka "Andre Malo <ndparker@gmx.net>"

Bugs

No bugs, of course. ;-) But if you’ve found one or have an idea how to improve rCSSmin, feel free to send a pull request on github or send a mail to <rcssmin-bugs@perlig.de>.

Author Information

rCSSmin was written and is maintained by André Malo.

Trivia / Fun

rCSSmin analyzes the CSS input using a simple regular expression, which looks like this:

pattern = (
    r'([^\\"\047u>@\r\n\f\040\t/;:{}]+)|(?<=[{}(=:>+[,!])((?:[\r\n\f\040'
    r'\t]|(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/))+)|^((?:[\r\n\f\040\t]|(?:/'
    r'\*[^*]*\*+(?:[^/*][^*]*\*+)*/))+)|((?:[\r\n\f\040\t]|(?:/\*[^*]*\*'
    r'+(?:[^/*][^*]*\*+)*/))+)(?=(([:{});=>+\],!])|$)?)|;((?:[\r\n\f\040'
    r'\t]|(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/))*(?:;(?:[\r\n\f\040\t]|(?:/'
    r'\*[^*]*\*+(?:[^/*][^*]*\*+)*/))*)*)(?=(\})?)|(\{)|(\})|((?:(?:\047'
    r'[^\047\\\r\n\f]*(?:\\[^\r\n\f][^\047\\\r\n\f]*)*\047)|(?:"[^"\\\r\n'
    r'\f]*(?:\\[^\r\n\f][^"\\\r\n\f]*)*")))|(?<![^\000-\054\056\057\072-'
    r'\100\133-\136\140\173-\177])url\([\r\n\f\040\t]*((?:(?:\047[^\047'
    r'\\]*(?:\\(?:[^\r]|\r\n?)[^\047\\]*)*\047)|(?:"[^"\\]*(?:\\(?:[^\r]'
    r'|\r\n?)[^"\\]*)*"))|(?:(?:[^\000-\040"\047()\\\177]*(?:(?:\\(?:[0-'
    r'9a-fA-F]{1,6}(?:[\040\n\t\f]|\r\n?)?|[^\n\r\f0-9a-fA-F]))[^\000-\0'
    r'40"\047()\\\177]*)*)(?:(?:[\r\n\f\040\t]+|(?:\\(?:[\n\f]|\r\n?))+)'
    r'(?:(?:[^\000-\040"\047()\\\177]|(?:\\(?:[0-9a-fA-F]{1,6}(?:[\040\n'
    r'\t\f]|\r\n?)?|[^\n\r\f0-9a-fA-F]))|(?:\\(?:[\n\f]|\r\n?)))[^\000-'
    r'\040"\047()\\\177]*(?:(?:\\(?:[0-9a-fA-F]{1,6}(?:[\040\n\t\f]|\r\n'
    r'?)?|[^\n\r\f0-9a-fA-F]))[^\000-\040"\047()\\\177]*)*)+)*))[\r\n\f'
    r'\040\t]*\)|(@(?:[mM][eE][dD][iI][aA]|[sS][uU][pP][pP][oO][rR][tT]['
    r'sS]|[dD][oO][cC][uU][mM][eE][nN][tT]|(?:-(?:[wW][eE][bB][kK][iI][t'
    r'T]|[mM][oO][zZ]|[oO]|[mM][sS])-)?[kK][eE][yY][fF][rR][aA][mM][eE]['
    r'sS]))(?![^\000-\054\056\057\072-\100\133-\136\140\173-\177])|((?:>'
    r'/\*\*/))((?:[\r\n\f\040\t]|(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/))*)|('
    r':[fF][iI][rR][sS][tT]-[lL](?:[iI][nN][eE]|[eE][tT][tT][eE][rR]))(('
    r'?:[\r\n\f\040\t]|(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/))*)(?=[{,])|((?'
    r':(?:\047[^\047\\\r\n\f]*(?:\\(?:[^\r]|\r\n?)[^\047\\\r\n\f]*)*\047'
    r')|(?:"[^"\\\r\n\f]*(?:\\(?:[^\r]|\r\n?)[^"\\\r\n\f]*)*")))|((?:\\('
    r'?:[0-9a-fA-F]{1,6}(?:[\040\n\t\f]|\r\n?)?|[^\n\r\f0-9a-fA-F]))[^'
    r'\\"\047u>@\r\n\f\040\t/;:{}]*)'
)