cssdecl Python CSS declaration computer

This package provides basic computation of CSS declarations in order to:

• handle overwriting of properties

  >>> from cssdecl import CSS22Resolver
  >>> resolve = CSS22Resolver().resolve_string
  >>> resolve('font-size: 10pt; font-size: 12pt')
  {'font-size': '12pt'}

• expand shorthands like border-width: 0 5pt

  >>> resolved = resolve('border-width: 0 5pt')
  >>> resolved.pop('border-left-width')
  '5pt'
  >>> resolved.pop('border-right-width')
  '5pt'
  >>> resolved.pop('border-bottom-width')
  '0pt'
  >>> resolved.pop('border-top-width')
  '0pt'
  >>> resolved
  {}

• (TODO!) expand shorthands like font: 5px sans-serif bold into font-family: sans-serif, font-size: 5px, font-weight: bold

• resolve sizes to a common unit (i.e. pt)

  >>> resolve('font-size: 20px')
  {'font-size': '15pt'}
  >>> resolve('font-size: 1em')
  {'font-size': '12pt'}
  >>> resolve('font-size: 1em', inherited={'font-size': '20pt'})
  {'font-size': '20pt'}
  >>> resolve('font-size: small')
  {'font-size': '9.600000pt'}

• resolve inherit given some inherited declarations

  >>> resolve('color: red; color: inherit', inherited={'color': 'blue'})
  {'color': 'blue'}

Some properties that are not shorthands in CSS 2.2 become shorthands in CSS 3, such as text-decoration. We therefore hope to provide cssdecl.CSS22Resolver and cssdecl.CSS3Resolver.

This module does not process CSS selectors (e.g. #some-id > * > div.some-class) and their applicability to elements, including specificity (e.g. !important).

This was first developed for use in Pandas (#15530). Issues will continue to be prioritised to improve CSS support there, in the absence of other clear use-cases.