appypod-rattail/px/px_parser.py

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# ------------------------------------------------------------------------------
from appy.shared.xml_parser import XmlEnvironment, XmlParser
from appy.pod.buffers import MemoryBuffer
# ------------------------------------------------------------------------------
class PxEnvironment(XmlEnvironment):
'''Environment for the PX parser.'''
def __init__(self):
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# In the following buffer, we will create a single memory sub-buffer
# that will hold the result of parsing the PX = a hierarchy of memory
# buffers = PX's AST (Abstract Syntax Tree).
# A major difference between POD and PX: POD creates the AST and
# generates the result in the same step: one AST is generated, and then
# directly produces a single evaluation, in the root file buffer. PX
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# works in 2 steps: the AST is initially created in self.ast. Then,
# several (concurrent) evaluations can occur, without re-generating the
# AST.
self.ast = MemoryBuffer(self, None)
# Buffer where we must dump the content we are currently reading
self.currentBuffer = self.ast
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# Tag content we are currently reading. We will put something in this
# attribute only if we encounter content that is Python code.
# Else, we will directly dump the parsed content into the current
# buffer.
self.currentContent = ''
# The currently walked element. We redefine it here. This attribute is
# normally managed by the parent XmlEnvironment, but we do not use the
# standard machinery from this environmment and from the default
# XmlParser for better performance. Indeed, the base parser and env
# process namespaces, and we do not need this for the PX parser.
self.currentElem = None
def addSubBuffer(self):
subBuffer = self.currentBuffer.addSubBuffer()
self.currentBuffer = subBuffer
def isActionElem(self, elem):
'''Returns True if the currently walked p_elem is the same elem as the
main buffer elem.'''
action = self.currentBuffer.action
return action and (action.elem == elem)
# ------------------------------------------------------------------------------
class PxParser(XmlParser):
'''PX parser that is specific for parsing PX data.'''
pxAttributes = ('var', 'for', 'if')
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# No-end tags
noEndTags = ('br', 'img', 'link', 'input')
noDumpTags = ('selected', 'checked')
def __init__(self, env, caller=None):
XmlParser.__init__(self, env, caller)
def startElement(self, elem, attrs):
'''A start p_elem with p_attrs is encountered in the PX.'''
e = self.env
self.currentElem = elem
# See if we have a PX attribute among p_attrs.
found = False
for name in self.pxAttributes:
if attrs.has_key(name):
if not found:
# This is the first PX attr we find.
# Create a sub-buffer with an action.
e.addSubBuffer()
found = True
# Add the action.
e.currentBuffer.createPxAction(elem, name, attrs[name])
if e.isActionElem(elem):
# Add a temp element in the buffer (that will be unreferenced
# later). This way, when encountering the corresponding end element,
# we will be able to check whether the end element corresponds to
# the main element or to a sub-element.
e.currentBuffer.addElement(elem, elemType='px')
if elem != 'x':
# Dump the start elements and its attributes. But as a preamble,
# manage special attributes that could not be dumped at all, like
# "selected" or "checked".
hook = None
ignorableAttrs = self.pxAttributes
for name in self.noDumpTags:
if attrs.has_key(name) and attrs[name].startswith(':'):
hook = (name, attrs[name][1:])
ignorableAttrs += (name,)
break
e.currentBuffer.dumpStartElement(elem, attrs,
ignoreAttrs=ignorableAttrs, noEndTag=elem in self.noEndTags,
hook=hook)
def endElement(self, elem):
e = self.env
# Manage the potentially collected Python expression in
# e.currentContent.
if e.currentContent:
e.currentBuffer.addExpression(e.currentContent)
e.currentContent = ''
# Dump the end element into the current buffer
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if (elem != 'x') and (elem not in self.noEndTags):
e.currentBuffer.dumpEndElement(elem)
# If this element is the main element of the current buffer, we must
# pop it and continue to work in the parent buffer.
if e.isActionElem(elem):
# Is it the buffer main element?
isMainElement = e.currentBuffer.isMainElement(elem)
# Unreference the element among buffer.elements
e.currentBuffer.unreferenceElement(elem)
if isMainElement:
# Continue to work in the parent buffer
e.currentBuffer = e.currentBuffer.parent
def characters(self, content):
e = self.env
if not e.currentContent and content.startswith(':'):
# This content is not static content to dump as-is into the result:
# it is a Python expression.
e.currentContent += content[1:]
elif e.currentContent:
# We continue to dump the Python expression.
e.currentContent += content
else:
e.currentBuffer.dumpContent(content)
# ------------------------------------------------------------------------------