validate.py

from __future__ import print_function
from collections import namedtuple, defaultdict

Check = namedtuple('Check', 'description check')
Condition = namedtuple('Condition', 'severity format')
Failure = namedtuple('Failure', 'type severity message data')

class Validator(object):
    def __init__(self):
        self.checks = []
        self.conditions = {}

    def condition(self, name, severity, format):
        if severity not in ('error', 'warning'):
            raise ValueError()
        self.conditions[name] = Condition(severity=severity,
                                          format=format)

    def check(self, description):
        def wrapper(fn):
            self.checks.append(Check(description = description,
                                     check = fn))
            return fn
        return wrapper

    def suppress(self, condition):
        self.conditions[condition] = \
          self.conditions[condition]._replace(severity='warning')

    def validate(self, value, suppress=[]):
        failures = []
        severity_counts = defaultdict(lambda: 0)
        def notify(condition, **kwargs):
            if condition in suppress:
                return
            cnd = self.conditions.get(condition)
            if cnd.severity is None:
                raise KeyError("Unknown failure mode: {}".format(condition))
            severity_counts[cnd.severity] += 1
            failures.append(Failure(type = condition,
                                    severity = cnd.severity,
                                    message = cnd.format.format(**kwargs),
                                    data = kwargs))
        for check in self.checks:
            check.check(value, notify)
        return severity_counts['error'] == 0, failures

# Example, very-reduced compstate

compstate_validator = Validator()
compstate_validator.condition('match-non-existent-team',
                              'error',
                              'Match {match} contains non-existent team {team}.')

@compstate_validator.check('all matches are populated with extant teams')
def check_extant_teams(state, notify):
    for match_number, match in enumerate(state['matches']):
        for team in match:
            if team is not None and team not in state['teams']:
                notify('match-non-existent-team',
                       match=match_number,
                       team=team)

compstate = {'teams': ['RWD', 'RGS'],
             'matches': [['RWD', 'RGS', None, 'TTN']]}
test_result, failures = compstate_validator.validate(compstate)
print("Validation {}".format("PASSED" if test_result else "FAILED"))
for failure in failures:
    print("[{}]: {}".format(failure.severity, failure.message))