PEP: 306
Title: How to Change Python's Grammar
Version: $Revision$
Last-Modified: $Date$
Author: Michael Hudson <mwh@python.net>
Status: Active
Type: Informational
Content-Type: text/plain
Created: 29-Jan-2003
Post-History: 30-Jan-2003


Abstract

    There's more to changing Python's grammar than editing
    Grammar/Grammar and Python/compile.c.  This PEP aims to be a
    checklist of places that must also be fixed.

    It is probably incomplete.  If you see omissions, just add them if
    you can -- you are not going to offend the author's sense of
    ownership.  Otherwise submit a bug or patch and assign it to mwh.

    This PEP is not intended to be an instruction manual on Python
    grammar hacking, for several reasons.


Rationale

    People are getting this wrong all the time; it took well over a
    year before someone noticed[1] that adding the floor division
    operator (//) broke the parser module.


Checklist

    __ Grammar/Grammar: OK, you'd probably worked this one out :)

    __ Python/compile.c: you'll most likely need to edit both the
       actual compiler and the symtable builder (which is to say both
       the com_foo and the sym_foo functions).

    __ You may need to regenerate Lib/symbol.py and/or Lib/token.py.

    __ The parser module.  Add some of your new syntax to test_parser,
       bang on parsermodule.c until it passes.

    __ The compiler package.  A good test is to compile the standard
       library and test suite with the compiler package and then check
       it runs.  You did add some of your new syntax to the test
       suite, didn't you?  There's a script in Tools/compiler that
       does this.

    __ If you've gone so far as to change the token structure of
       Python, then the tokenizer library module will need to be
       changed.

    __ Certain changes may require tweaks to the library module
       pycblr.

    __ Jython too will need work, but I don't know what.  Explanations
       gratefully received.


References

    [1] SF Bug #676521, parser module validation failure
        http://www.python.org/sf/676521


Copyright

    This document has been placed in the public domain.



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