# # Tree visitor and transform framework # import inspect import Nodes import ExprNodes import Naming from StringEncoding import EncodedString class BasicVisitor(object): """A generic visitor base class which can be used for visiting any kind of object.""" # Note: If needed, this can be replaced with a more efficient metaclass # approach, resolving the jump table at module load time rather than per visitor # instance. def __init__(self): self.dispatch_table = {} def visit(self, obj): cls = obj.__class__ m = self.dispatch_table.get(cls.__name__) if m is None: # Must resolve, try entire hierarchy pattern = "visit_%s" mro = inspect.getmro(cls) for cls in mro: m = getattr(self, pattern % cls.__name__, None) if m is not None: break else: print type(self), type(obj) print self.access_path print self.access_path[-1][0].pos print self.access_path[-1][0].__dict__ raise RuntimeError("Visitor does not accept object: %s" % obj) self.dispatch_table[cls.__name__] = m return m(obj) class TreeVisitor(BasicVisitor): """ Base class for writing visitors for a Cython tree, contains utilities for recursing such trees using visitors. Each node is expected to have a child_attrs iterable containing the names of attributes containing child nodes or lists of child nodes. Lists are not considered part of the tree structure (i.e. contained nodes are considered direct children of the parent node). visit_children visits each of the children of a given node (see the visit_children documentation). When recursing the tree using visit_children, an attribute access_path is maintained which gives information about the current location in the tree as a stack of tuples: (parent_node, attrname, index), representing the node, attribute and optional list index that was taken in each step in the path to the current node. Example: >>> class SampleNode: ... child_attrs = ["head", "body"] ... def __init__(self, value, head=None, body=None): ... self.value = value ... self.head = head ... self.body = body ... def __repr__(self): return "SampleNode(%s)" % self.value ... >>> tree = SampleNode(0, SampleNode(1), [SampleNode(2), SampleNode(3)]) >>> class MyVisitor(TreeVisitor): ... def visit_SampleNode(self, node): ... print "in", node.value, self.access_path ... self.visitchildren(node) ... print "out", node.value ... >>> MyVisitor().visit(tree) in 0 [] in 1 [(SampleNode(0), 'head', None)] out 1 in 2 [(SampleNode(0), 'body', 0)] out 2 in 3 [(SampleNode(0), 'body', 1)] out 3 out 0 """ def __init__(self): super(TreeVisitor, self).__init__() self.access_path = [] def visitchild(self, child, parent, attrname, idx): self.access_path.append((parent, attrname, idx)) result = self.visit(child) self.access_path.pop() return result def visitchildren(self, parent, attrs=None): """ Visits the children of the given parent. If parent is None, returns immediately (returning None). The return value is a dictionary giving the results for each child (mapping the attribute name to either the return value or a list of return values (in the case of multiple children in an attribute)). """ if parent is None: return None result = {} for attr in parent.child_attrs: if attrs is not None and attr not in attrs: continue child = getattr(parent, attr) if child is not None: if isinstance(child, list): childretval = [self.visitchild(x, parent, attr, idx) for idx, x in enumerate(child)] else: childretval = self.visitchild(child, parent, attr, None) assert not isinstance(childretval, list), 'Cannot insert list here: %s in %r' % (attr, parent) result[attr] = childretval return result class VisitorTransform(TreeVisitor): """ A tree transform is a base class for visitors that wants to do stream processing of the structure (rather than attributes etc.) of a tree. It implements __call__ to simply visit the argument node. It requires the visitor methods to return the nodes which should take the place of the visited node in the result tree (which can be the same or one or more replacement). Specifically, if the return value from a visitor method is: - [] or None; the visited node will be removed (set to None if an attribute and removed if in a list) - A single node; the visited node will be replaced by the returned node. - A list of nodes; the visited nodes will be replaced by all the nodes in the list. This will only work if the node was already a member of a list; if it was not, an exception will be raised. (Typically you want to ensure that you are within a StatListNode or similar before doing this.) """ def visitchildren(self, parent, attrs=None): result = super(VisitorTransform, self).visitchildren(parent, attrs) for attr, newnode in result.iteritems(): if not isinstance(newnode, list): setattr(parent, attr, newnode) else: # Flatten the list one level and remove any None newlist = [] for x in newnode: if x is not None: if isinstance(x, list): newlist += x else: newlist.append(x) setattr(parent, attr, newlist) return result def __call__(self, root): return self.visit(root) class CythonTransform(VisitorTransform): """ Certain common conventions and utilitues for Cython transforms. """ def __init__(self, context): super(CythonTransform, self).__init__() self.context = context def __call__(self, node): import ModuleNode if isinstance(node, ModuleNode.ModuleNode): self.current_directives = node.directives return super(CythonTransform, self).__call__(node) def visit_CompilerDirectivesNode(self, node): old = self.current_directives self.current_directives = node.directives self.visitchildren(node) self.current_directives = old return node def visit_Node(self, node): self.visitchildren(node) return node # Utils def ensure_statlist(node): if not isinstance(node, Nodes.StatListNode): node = Nodes.StatListNode(pos=node.pos, stats=[node]) return node def replace_node(ptr, value): """Replaces a node. ptr is of the form used on the access path stack (parent, attrname, listidx|None) """ parent, attrname, listidx = ptr if listidx is None: setattr(parent, attrname, value) else: getattr(parent, attrname)[listidx] = value class PrintTree(TreeVisitor): """Prints a representation of the tree to standard output. Subclass and override repr_of to provide more information about nodes. """ def __init__(self): TreeVisitor.__init__(self) self._indent = "" def indent(self): self._indent += " " def unindent(self): self._indent = self._indent[:-2] def __call__(self, tree, phase=None): print("Parse tree dump at phase '%s'" % phase) self.visit(tree) return tree # Don't do anything about process_list, the defaults gives # nice-looking name[idx] nodes which will visually appear # under the parent-node, not displaying the list itself in # the hierarchy. def visit_Node(self, node): if len(self.access_path) == 0: name = "(root)" else: parent, attr, idx = self.access_path[-1] if idx is not None: name = "%s[%d]" % (attr, idx) else: name = attr print("%s- %s: %s" % (self._indent, name, self.repr_of(node))) self.indent() self.visitchildren(node) self.unindent() return node def repr_of(self, node): if node is None: return "(none)" else: result = node.__class__.__name__ if isinstance(node, ExprNodes.NameNode): result += "(type=%s, name=\"%s\")" % (repr(node.type), node.name) elif isinstance(node, Nodes.DefNode): result += "(name=\"%s\")" % node.name elif isinstance(node, ExprNodes.ExprNode): t = node.type result += "(type=%s)" % repr(t) return result if __name__ == "__main__": import doctest doctest.testmod()