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parsenode.py
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parsenode.py
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#
# $Id: parsenode.py 14 2012-06-07 02:46:19Z nickw $
#
# NAME: parsenode.py
#
# AUTHOR: Nick Whalen <[email protected]>
# COPYRIGHT: 2012 by Nick Whalen
# LICENSE:
# 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.
#
# DESCRIPTION:
# Defines ParseNode, which acts as the base for grammar-based parsers. This isn't an ideal class, but it works for
# many things. It spun out of my need to parse iproute2 grammars, so bear that in mind.
#
from lib import orderedset
class ParseNode(object):
raw_data = '' # The node's raw, text data
next_data = None # Data which will be passed to the child nodes of this node
child_classes = orderedset.OrderedSet() # Ordered list of the parser nodes 'under' this node (child_classes)
children = {}
def __init__(self, tokens, child_class_list = list()):
"""
Constructor. Calls meth:parse to parse the incoming tokens and then adds any child nodes.
:param tokens: List of text tokens to parse
:param child_class_list: List of child classes to parse token lists
"""
# The token list can potentially be empty (not all grammar options are used)
if tokens:
self.next_data = self.parse(tokens) # Call the child class' parser
if child_class_list:
self.addChildren(child_class_list, self.next_data)
#---
def __str__(self):
return self.raw_data
#---
# Dictionary type getter/setters
def __getitem__(self, item):
"""
Getter for dictionary style operation. Supports class variables and referencing child classes by their class
names.
:param item: String
"""
try:
return self.__dict__[item]
# If the item doesn't exist, see if it matches a child's name
except KeyError:
if item in self.children:
return self.children[item]
else:
raise
#---
def __setitem__(self, key, value):
"""
Setter for dictionary style operation. Supports class variables and referencing child classes by their class
names.
:param key: String
:param value: String
"""
try:
self.__dict__[key] = value
except KeyError:
if key in self.children:
self.children[key] = value
else:
raise
#---
def __delitem__(self, key):
"""
Deletion operator for dictionary style operation. Supports class variables and referencing child classes by
their class names.
:param key: String
"""
try:
del self.__dict__[key]
except KeyError:
if key in self.children:
del self.children[key]
else:
raise
#---
# Simply adds a segment to self.raw_data with the proper spacing
def _addRawSegment(self, segment): self.raw_data += "%s " %segment
def addChildren(self, nodes, node_data):
"""
Adds children to the child_classes ordered set.
:param nodes: List of instances of class:ParseNode
"""
data = node_data
for node in nodes:
# Instantiate the grammar node
new_node = node(data)
# Save the new, instantiated node in a dict by it's class name
self.children[new_node.__class__.__name__] = new_node
# Save unused data to be used by next node
data = new_node.next_data
#---
#---