| """API for traversing the AST nodes. Implemented by the compiler and |
| meta introspection. |
| """ |
| import typing as t |
| |
| from .nodes import Node |
| |
| if t.TYPE_CHECKING: |
| import typing_extensions as te |
| |
| class VisitCallable(te.Protocol): |
| def __call__(self, node: Node, *args: t.Any, **kwargs: t.Any) -> t.Any: |
| ... |
| |
| |
| class NodeVisitor: |
| """Walks the abstract syntax tree and call visitor functions for every |
| node found. The visitor functions may return values which will be |
| forwarded by the `visit` method. |
| |
| Per default the visitor functions for the nodes are ``'visit_'`` + |
| class name of the node. So a `TryFinally` node visit function would |
| be `visit_TryFinally`. This behavior can be changed by overriding |
| the `get_visitor` function. If no visitor function exists for a node |
| (return value `None`) the `generic_visit` visitor is used instead. |
| """ |
| |
| def get_visitor(self, node: Node) -> "t.Optional[VisitCallable]": |
| """Return the visitor function for this node or `None` if no visitor |
| exists for this node. In that case the generic visit function is |
| used instead. |
| """ |
| return getattr(self, f"visit_{type(node).__name__}", None) |
| |
| def visit(self, node: Node, *args: t.Any, **kwargs: t.Any) -> t.Any: |
| """Visit a node.""" |
| f = self.get_visitor(node) |
| |
| if f is not None: |
| return f(node, *args, **kwargs) |
| |
| return self.generic_visit(node, *args, **kwargs) |
| |
| def generic_visit(self, node: Node, *args: t.Any, **kwargs: t.Any) -> t.Any: |
| """Called if no explicit visitor function exists for a node.""" |
| for child_node in node.iter_child_nodes(): |
| self.visit(child_node, *args, **kwargs) |
| |
| |
| class NodeTransformer(NodeVisitor): |
| """Walks the abstract syntax tree and allows modifications of nodes. |
| |
| The `NodeTransformer` will walk the AST and use the return value of the |
| visitor functions to replace or remove the old node. If the return |
| value of the visitor function is `None` the node will be removed |
| from the previous location otherwise it's replaced with the return |
| value. The return value may be the original node in which case no |
| replacement takes place. |
| """ |
| |
| def generic_visit(self, node: Node, *args: t.Any, **kwargs: t.Any) -> Node: |
| for field, old_value in node.iter_fields(): |
| if isinstance(old_value, list): |
| new_values = [] |
| for value in old_value: |
| if isinstance(value, Node): |
| value = self.visit(value, *args, **kwargs) |
| if value is None: |
| continue |
| elif not isinstance(value, Node): |
| new_values.extend(value) |
| continue |
| new_values.append(value) |
| old_value[:] = new_values |
| elif isinstance(old_value, Node): |
| new_node = self.visit(old_value, *args, **kwargs) |
| if new_node is None: |
| delattr(node, field) |
| else: |
| setattr(node, field, new_node) |
| return node |
| |
| def visit_list(self, node: Node, *args: t.Any, **kwargs: t.Any) -> t.List[Node]: |
| """As transformers may return lists in some places this method |
| can be used to enforce a list as return value. |
| """ |
| rv = self.visit(node, *args, **kwargs) |
| |
| if not isinstance(rv, list): |
| return [rv] |
| |
| return rv |