# Τεκμηρίωση του Django - 1.10.7

# Πηγαίος κώδικας για το django.core.checks.registry

    # -*- coding: utf-8 -*-
    from __future__ import unicode_literals

    from itertools import chain

    from django.utils.itercompat import is_iterable

    class Tags(object):
        """
        Built-in tags for internal checks.
        """
        admin = 'admin'
        caches = 'caches'
        compatibility = 'compatibility'
        database = 'database'
        models = 'models'
        security = 'security'
        signals = 'signals'
        templates = 'templates'
        urls = 'urls'

    class CheckRegistry(object):

        def __init__(self):
            self.registered_checks = []
            self.deployment_checks = []

        def register(self, check=None, *tags, **kwargs):
            """
            Can be used as a function or a decorator. Register given function
            `f` labeled with given `tags`. The function should receive **kwargs
            and return list of Errors and Warnings.

            Example::

                registry = CheckRegistry()
                @registry.register('mytag', 'anothertag')
                def my_check(apps, **kwargs):
                    # ... perform checks and collect `errors` ...
                    return errors
                # or
                registry.register(my_check, 'mytag', 'anothertag')
            """
            kwargs.setdefault('deploy', False)

            def inner(check):
                check.tags = tags
                if kwargs['deploy']:
                    if check not in self.deployment_checks:
                        self.deployment_checks.append(check)
                elif check not in self.registered_checks:
                    self.registered_checks.append(check)
                return check

            if callable(check):
                return inner(check)
            else:
                if check:
                    tags += (check, )
                return inner

        def run_checks(self, app_configs=None, tags=None, include_deployment_checks=False):
            """
            Run all registered checks and return list of Errors and Warnings.
            """
            errors = []
            checks = self.get_checks(include_deployment_checks)

            if tags is not None:
                checks = [check for check in checks
                          if hasattr(check, 'tags') and set(check.tags) & set(tags)]
            else:
                # By default, 'database'-tagged checks are not run as they do more
                # than mere static code analysis.
                checks = [check for check in checks
                          if not hasattr(check, 'tags') or Tags.database not in check.tags]

            for check in checks:
                new_errors = check(app_configs=app_configs)
                assert is_iterable(new_errors), (
                    "The function %r did not return a list. All functions registered "
                    "with the checks registry must return a list." % check)
                errors.extend(new_errors)
            return errors

        def tag_exists(self, tag, include_deployment_checks=False):
            return tag in self.tags_available(include_deployment_checks)

        def tags_available(self, deployment_checks=False):
            return set(chain(*[check.tags for check in self.get_checks(deployment_checks) if hasattr(check, 'tags')]))

        def get_checks(self, include_deployment_checks=False):
            checks = list(self.registered_checks)
            if include_deployment_checks:
                checks.extend(self.deployment_checks)
            return checks

    registry = CheckRegistry()
    register = registry.register
    run_checks = registry.run_checks
    tag_exists = registry.tag_exists