如何使用额外的方法在 Sage 中创建新的 Graph 类？
我正在 Sage 中编写一些代码来使用费曼图进行一些计算，费曼图只是带有边缘标签的有限的、无向的多重图。我需要实现边缘收缩等方法，而 sage.graphs.graph.Graph 类中奇怪地缺少这些方法。但我也想继承所有现有的图形方法，例如 is_tree。
这是模块 Feynman.sage 的顶部，应该附加新类。
from sage.graphs.graph import Graph
class FeynmanGraph(Graph):
"""An unoriented multi-graph with labeled edges"""
def __init__(self, E=[]):
self._edges = len(E)
def __repr__(self):
return 'A Feynman graph with ' + str(self._edges) + ' edges.'
我没有做正确的事情。虽然类的实例化产生了正确的方法目录，但其中许多方法不起作用，因为
'FeynmanGraph' object has no attribute '_backend'
我认为这与 Sage 只是其他一些图论包的 Pythonic 包装器有关。
请指教。
I am writing some code in Sage to do some calculations with Feynman graphs, which are just finite, un-oriented multigraphs with edge-labels. I need to implement methods such as edge-contraction, which are curiously missing from the class sage.graphs.graph.Graph. But I also want to inherit all the existing graph methods, like e.g. is_tree.
Here's the top of the module Feynman.sage that ought to attach the new class.
from sage.graphs.graph import Graph
class FeynmanGraph(Graph):
"""An unoriented multi-graph with labeled edges"""
def __init__(self, E=[]):
self._edges = len(E)
def __repr__(self):
return 'A Feynman graph with ' + str(self._edges) + ' edges.'
I'm not doing something right. Although an instantiation of the class yields the correct directory of methods, many of them don't work because
'FeynmanGraph' object has no attribute '_backend'
I think this has something to do with the way that Sage is just a Pythonic wrapper for some other graph theory package.
Please advise.
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您可能根本没有正确继承事物。尝试将其插入到
__init__()的开头：You might simply not be inheriting things correctly. Try inserting this at the beginning of
__init__():