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peggy

A simple PEG parser generator, focused on python's grammar. Mostly a wrapper for pegen as it exists in the cpython source.

peggy is different from the pegen package (which is a different code base) in that it directly uses python.gram from the cpython source. The problem with doing that is that all actions in that grammar are written for C code. For example:

# Class definitions
# -----------------

class_def[stmt_ty]:
    | a=decorators b=class_def_raw { _PyPegen_class_def_decorators(p, a, b) }
    | class_def_raw

class_def_raw[stmt_ty]:
    | invalid_class_def_raw
    | 'class' a=NAME t=[type_params] b=['(' z=[arguments] ')' { z }] ':' c=block {
        _PyAST_ClassDef(a->v.Name.id,
                     (b) ? ((expr_ty) b)->v.Call.args : NULL,
                     (b) ? ((expr_ty) b)->v.Call.keywords : NULL,
                     c, NULL, t, EXTRA) }

peggy makes this work by stripping all return types and actions from the grammar. Instead of actions, it returns the name of the rule it matched in addition to the matched tokens. This makes it useful if you just care about rules, which is all pyxy needs.

Summary

Disadvantages

  • Can't differentiate between different cases of a rule that's matched
  • Output data structure isn't the easiest to work with

Advantages

  • Uses the canonical Python grammar
  • Can differentiate based on rule