Source code for lale.util.VisitorMeta

# Copyright 2019 IBM Corporation
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from abc import ABCMeta


class VisitorMeta(type):
    """This meta class adds a private _accept method that calls visitCLASSNAME on the visitor.
    It does not currently support inheritance: you need to define the visitC method for subclasses
    explicitly.
    The private _accept method should be called via the Visitor#acccept method
    """

    def __init__(cls, *args, **kwargs):
        super(VisitorMeta, cls).__init__(*args, **kwargs)

        method_name = getattr(cls, "__name__", "???")
        # ensure that only idenifiers are used
        if not isinstance(method_name, str) or not method_name.isidentifier():
            method_name = "???"

        selector = f"""
        from lale.util import VisitorPathError
        try:
            return visitor.visit{method_name}(self, *args, **kwargs)
        except VisitorPathError as e:
            e.push_parent_path(self)
            raise
        except BaseException as e:
            raise VisitorPathError([self]) from e
        """
        _accept_code = f"def _accept(self, visitor, *args, **kwargs):\n\t{selector}"
        ll = {}
        # This is safe since the only user manipulatable part of the code is
        # cls.__name__, which we sanitize to ensure that it is a valid identifier
        exec(_accept_code, globals(), ll)  # nosec
        setattr(cls, "_accept", ll["_accept"])


class AbstractVisitorMeta(VisitorMeta, ABCMeta):
    """This meta class adds an _accept method that calls visitCLASSNAME on the visitor.
    It does not currently support inheritance: you need to define the visitC method for subclasses
    explicitly.
    The private _accept method should be called via the Visitor#acccept method.
    """

    def __init__(cls, *args, **kwargs):
        super(AbstractVisitorMeta, cls).__init__(*args, **kwargs)