Something about matching for trafaret

match.py

import trafaret as t


groups = [
    {'service': [{'guid': 'bla'}]},
    {'service': []},
]


class Match(t.Trafaret):
    def __init__(self, trafaret, first=True):
        self.first = first
        self.trafaret = t.ensure_trafaret(trafaret)

    def transform(self, iterable, context=None):
        res = []
        for item in iterable:
            try:
                matched = self.trafaret(item)
                if self.first:
                    return matched
                else:
                    res.append(matched)
            except t.DataError:
                pass
        if not res:
            raise t.DataError('No match')
        return res


tt = (
    Match(t.Dict(service=Match(t.Dict(guid=t.Atom('bla')))))
    & (lambda match: match['service'])
)


assert tt(groups) == {'guid': 'bla'}