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From WHATWG Wiki
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HTML5Lib is a project to create a Python-based implementation of various parts of the WHATWG spec, in particular, a tokeniser and parser. It is not an offical WHATWG project, however we plan to use this wiki to document and discuss the library design. The code is avaliable under an open-source MIT license.

Project Page

Google code project page

Design Issues


The tokeniser is controlled by a single Tokeniser class. It emits tokens which are subclasses of the Token class. At some level it needs to be possible to store information about the token being emitted as the tree builder sometimes need to reprocess a token, however there may be some opportunity to economize here.


getToken - return the next token.


The current tokeniser state is stored in the state attribute. Each state corresponds to a single method on the Tokeniser object. The states attributes maps state names to methods.

Occasionally, parsing will result in characters being read multiple times from the stream. Therefore a queue is used to buffer characters that have been read from the file but need to be reprocessed (do we need to buffer multiple characters? Will support for a trailing slash change this?).

During processing, any unfinished tokens are held in the token attribute and finished tokens in the tokenQueue.


  • Should keep track of line+col number for error reporting
  • Use of if statements in the states may be suboptimal (but we should time this)