pyg will be a PEG parser library formed as an internal Python DSL. it will be used in cramex, a copycat of cram with expect support.

The surface is heading to resemble Boost.Spirit: grammars are composed using a vaguely (xBNF/PEG)-like syntax enabled through operator overloading.

>>> from pyg import Rule, chr_, int_

>>> n = Rule('number')
>>> o = Rule('operator')
>>> e = Rule('expression')

>>> e %= n >> o >> n
>>> o %= chr_('+-')
>>> n %= int_

>>> e.matches('42 + 69')
True, None
>>> e.matches('69')
True, None
>>> e.matches('42 69')
False, "Failed on line 1 column 3:\n42 69\n  ^\n"