Tips/tricks/hints for writing new fixers:

    * Don't write your own PATTERN from scratch; that's what find_pattern.py
      is for.
    
    * If your fixer works by changing a node's children list or a leaf's
      value, be sure to call the node/leaf's changed() method. This to
      be sure refactor.py will recognize that the tree has changed.
      
    * If you're making changes to pgen2, tokenize or any other part of the
      parsing system (sometimes even pytree), you might want to check out
      the 'dummy' fixer. It doesn't make any changes to the file, so you
      just see what the parser does.


Putting 2to3 to work somewhere else:

    * By default, 2to3 uses a merger of Python 2.x and Python 3's grammars.
        If you want to support a different grammar, just replace the
        Grammar.txt file with Grammar/Grammar from your chosen Python version.

    * The real heart of 2to3 is the concrete syntax tree parser in pgen2; this
        chunk of the system is suitable for a wide range of applications that
        require CST transformation. All that's required is to rip off the fixer
        layer and replace it with something else that walks the tree. One
        application would be a tool to check/enforce style guidelines; this
        could leverage 90% of the existing infrastructure with primarily
        cosmetic changes (e.g., fixes/fix_*.py -> styles/style_*.py).

    * The examples/ directory contains fixers that show off 2to3's flexibility,
        such as a fixer for whitespace.


TODO

    Simple:
    #######
    
    * Refactor common code out of fixes/fix_*.py into fixes.util (on-going).


    Complex:
    ########
    
    * Replace tuple usage in patterns and node.children with lists (95%
        done). Simplify fixers accordingly (mostly done, I think).

    * Come up with a scheme to hide the details of suite indentation (some
        kind of custom pytree node for suites, probably). This will
        automatically reindent all code with spaces, tied into a refactor.py
        flag that allows you to specify the indent level.

    * Remove the need to explicitly assign a node's parent attribute.