def validate_ex(expected_schema,                  # type: Schema
                datum,                            # type: Any
                identifiers=None,                 # type: List[Text]
                strict=False,                     # type: bool
                foreign_properties=None,          # type: Set[Text]
                raise_ex=True,                    # type: bool
                strict_foreign_properties=False,  # type: bool
                logger=_logger,                   # type: logging.Logger
                skip_foreign_properties=False     # type: bool
                ):
    # type: (...) -> bool
    """Determine if a python datum is an instance of a schema."""

    if not identifiers:
        identifiers = []

    if not foreign_properties:
        foreign_properties = set()

    schema_type = expected_schema.type

    if schema_type == 'null':
        if datum is None:
            return True
        else:
            if raise_ex:
                raise ValidationException(u"the value is not null")
            else:
                return False
    elif schema_type == 'boolean':
        if isinstance(datum, bool):
            return True
        else:
            if raise_ex:
                raise ValidationException(u"the value is not boolean")
            else:
                return False
    elif schema_type == 'string':
        if isinstance(datum, six.string_types):
            return True
        elif isinstance(datum, bytes):
            datum = datum.decode(u"utf-8")
            return True
        else:
            if raise_ex:
                raise ValidationException(u"the value is not string")
            else:
                return False
    elif schema_type == 'int':
        if (isinstance(datum, six.integer_types)
                and INT_MIN_VALUE <= datum <= INT_MAX_VALUE):
            return True
        else:
            if raise_ex:
                raise ValidationException(u"`%s` is not int" % vpformat(datum))
            else:
                return False
    elif schema_type == 'long':
        if ((isinstance(datum, six.integer_types))
                and LONG_MIN_VALUE <= datum <= LONG_MAX_VALUE):
            return True
        else:
            if raise_ex:
                raise ValidationException(
                    u"the value `%s` is not long" % vpformat(datum))
            else:
                return False
    elif schema_type in ['float', 'double']:
        if (isinstance(datum, six.integer_types)
                or isinstance(datum, float)):
            return True
        else:
            if raise_ex:
                raise ValidationException(
                    u"the value `%s` is not float or double" % vpformat(datum))
            else:
                return False
    elif isinstance(expected_schema, avro.schema.EnumSchema):
        if expected_schema.name == "Any":
            if datum is not None:
                return True
            else:
                if raise_ex:
                    raise ValidationException(u"'Any' type must be non-null")
                else:
                    return False
        if not isinstance(datum, six.string_types):
            if raise_ex:
                raise ValidationException(
                    u"value is a %s but expected a string" % (type(datum).__name__))
            else:
                return False
        if expected_schema.name == "Expression":
            if "$(" in datum or "${" in datum:
                return True
            if raise_ex:
                raise ValidationException(u"value `%s` does not contain an expression in the form $() or ${}" % datum)
            else:
                return False
        if datum in expected_schema.symbols:
            return True
        else:
            if raise_ex:
                raise ValidationException(u"the value %s is not a valid %s, expected %s%s" % (vpformat(datum), expected_schema.name,
                                                                                              "one of " if len(
                                                                                                  expected_schema.symbols) > 1 else "",
                                                                                              "'" + "', '".join(expected_schema.symbols) + "'"))
            else:
                return False
    elif isinstance(expected_schema, avro.schema.ArraySchema):
        if isinstance(datum, MutableSequence):
            for i, d in enumerate(datum):
                try:
                    sl = SourceLine(datum, i, ValidationException)
                    if not validate_ex(expected_schema.items, d, identifiers,
                                       strict=strict,
                                       foreign_properties=foreign_properties,
                                       raise_ex=raise_ex,
                                       strict_foreign_properties=strict_foreign_properties,
                                       logger=logger,
                                       skip_foreign_properties=skip_foreign_properties):
                        return False
                except ValidationException as v:
                    if raise_ex:
                        raise sl.makeError(
                            six.text_type("item is invalid because\n%s" % (indent(str(v)))))
                    else:
                        return False
            return True
        else:
            if raise_ex:
                raise ValidationException(u"the value %s is not a list, expected list of %s" % (
                    vpformat(datum), friendly(expected_schema.items)))
            else:
                return False
    elif isinstance(expected_schema, avro.schema.UnionSchema):
        for s in expected_schema.schemas:
            if validate_ex(s, datum, identifiers, strict=strict, raise_ex=False,
                           strict_foreign_properties=strict_foreign_properties,
                           logger=logger, skip_foreign_properties=skip_foreign_properties):
                return True

        if not raise_ex:
            return False

        errors = []  # type: List[Text]
        checked = []
        for s in expected_schema.schemas:
            if isinstance(datum, MutableSequence) and not isinstance(s, avro.schema.ArraySchema):
                continue
            elif isinstance(datum, MutableMapping) and not isinstance(s, avro.schema.RecordSchema):
                continue
            elif (isinstance(  # type: ignore
                    datum, (bool, six.integer_types, float, six.string_types))
                    and isinstance(s, (avro.schema.ArraySchema,
                                       avro.schema.RecordSchema))):
                continue
            elif datum is not None and s.type == "null":
                continue

            checked.append(s)
            try:
                validate_ex(s, datum, identifiers, strict=strict,
                            foreign_properties=foreign_properties,
                            raise_ex=True,
                            strict_foreign_properties=strict_foreign_properties,
                            logger=logger, skip_foreign_properties=skip_foreign_properties)
            except ClassValidationException as e:
                raise
            except ValidationException as e:
                errors.append(six.text_type(e))
        if bool(errors):
            raise ValidationException(bullets(["tried %s but\n%s" % (friendly(
                checked[i]), indent(errors[i])) for i in range(0, len(errors))], "- "))
        else:
            raise ValidationException("value is a %s, expected %s" % (
                type(datum).__name__, friendly(expected_schema)))

    elif isinstance(expected_schema, avro.schema.RecordSchema):
        if not isinstance(datum, MutableMapping):
            if raise_ex:
                raise ValidationException(u"is not a dict")
            else:
                return False

        classmatch = None
        for f in expected_schema.fields:
            if f.name in ("class",):
                d = datum.get(f.name)
                if not d:
                    if raise_ex:
                        raise ValidationException(
                            u"Missing '%s' field" % (f.name))
                    else:
                        return False
                if expected_schema.name != d:
                    if raise_ex:
                        raise ValidationException(
                            u"Expected class '%s' but this is '%s'" % (expected_schema.name, d))
                    else:
                        return False
                classmatch = d
                break

        errors = []
        for f in expected_schema.fields:
            if f.name in ("class",):
                continue

            if f.name in datum:
                fieldval = datum[f.name]
            else:
                try:
                    fieldval = f.default
                except KeyError:
                    fieldval = None

            try:
                sl = SourceLine(datum, f.name, six.text_type)
                if not validate_ex(f.type, fieldval, identifiers, strict=strict,
                                   foreign_properties=foreign_properties,
                                   raise_ex=raise_ex,
                                   strict_foreign_properties=strict_foreign_properties,
                                   logger=logger, skip_foreign_properties=skip_foreign_properties):
                    return False
            except ValidationException as v:
                if f.name not in datum:
                    errors.append(u"missing required field `%s`" % f.name)
                else:
                    errors.append(sl.makeError(u"the `%s` field is not valid because\n%s" % (
                        f.name, indent(str(v)))))

        for d in datum:
            found = False
            for f in expected_schema.fields:
                if d == f.name:
                    found = True
            if not found:
                sl = SourceLine(datum, d, six.text_type)
                if d not in identifiers and d not in foreign_properties and d[0] not in ("@", "$"):
                    if (d not in identifiers and strict) and (
                            d not in foreign_properties and strict_foreign_properties and not skip_foreign_properties) and not raise_ex:
                        return False
                    split = urllib.parse.urlsplit(d)
                    if split.scheme:
                        if not skip_foreign_properties:
                            err = sl.makeError(u"unrecognized extension field `%s`%s.%s"
                                               % (d,
                                                  " and strict_foreign_properties checking is enabled"
                                                  if strict_foreign_properties else "",
                                                  "\nForeign properties from $schemas:\n  %s" % "\n  ".join(sorted(foreign_properties))
                                                  if len(foreign_properties) > 0 else ""))
                            if strict_foreign_properties:
                                errors.append(err)
                            elif len(foreign_properties) > 0:
                                logger.warning(strip_dup_lineno(err))
                    else:
                        err = sl.makeError(u"invalid field `%s`, expected one of: %s" % (
                            d, ", ".join("'%s'" % fn.name for fn in expected_schema.fields)))
                        if strict:
                            errors.append(err)
                        else:
                            logger.warning(err)

        if bool(errors):
            if raise_ex:
                if classmatch:
                    raise ClassValidationException(bullets(errors, "* "))
                else:
                    raise ValidationException(bullets(errors, "* "))
            else:
                return False
        else:
            return True
    if raise_ex:
        raise ValidationException(u"Unrecognized schema_type %s" % schema_type)
    else:
        return False