def __init__(self): """ Instantiate an empty tree. """ self.__contents = None self.__elements = SortedDict()
class ParseTree(object):
"""
A parse tree to model an expression parsing.
It is returned by the L{read<lect.Lect.read>} method of class C{Lect}.
"""
def __init__(self):
"""
Instantiate an empty tree.
"""
self.__contents = None
self.__elements = SortedDict()
def add_recognition(self, recognition):
"""
Add a list of expression parsings to the tree, calling the L{add} method.
@param recognition: A list of expression parsings.
@type recognition: list of C{(item, path)} tuples
"""
for item, path in recognition:
self.add(item, path)
def iter_children(self, path):
"""
Return an iterator to the subtrees below a given position.
@param path: A tree path.
@type path: list of str
@return: The child trees below a given position.
@rtype: iterator of ParseTree
"""
return self.__elements.items()
def subtree(self, path):
"""
Return the subtree at a given position.
@param path: A tree path.
@type path: list of str
@return: The child tree at given position.
@rtype: ParseTree
"""
st = self
for segm in path:
st = st.__elements[segm]
return st
def iter_items(self):
"""
Return an iterator to the items.
@rtype: iterator of items
"""
for i in self.__contents:
yield i
def add(self, item, path):
"""
Add an expression parsing to the tree.
If another item exists at the given position, the new item is appended, otherwise the new position is created with the item only.
@param item: An expression parsing.
@type item: C{(item, path)} tuples
@param path: A tree path.
@type path: list of str
"""
if len(path) == 0:
return
st = self
for segm in path:
if segm in st.__elements:
st = st.__elements[segm]
else:
nst = ParseTree()
st.__elements[segm] = nst
st = nst
if st.__contents is None:
st.__contents = [item]
else:
st.__contents.append(item)
def __repr__(self):
"""
Compute a representation for the parse tree.
@rtype: str
"""
s = []
if self.__elements:
s.append(Utilities.dict_str(self.__elements))
if self.__contents:
s.append(str(self.__contents))
return " = ".join(s)