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Visitor.py
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Visitor.py
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#
# 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()