Python 图
Python 图详细操作教程
图形是一组对象的图形表示，其中一些对象对通过链接连接。相互连接的对象由称为顶点的点表示，而连接这些顶点的链接称为边。与图相关的各种术语和功能在此处的教程中进行了详细描述。在本章中，我们将了解如何使用python程序创建图形并向其中添加各种数据元素。以下是我们在图形上执行的基本操作。
显示图顶点
显示图形边缘
添加一个顶点
添加边缘
创建图
使用python字典数据类型可以轻松呈现图形。我们将顶点表示为字典的键，并将顶点之间的连接也称为边作为字典中的值。
Take a look at the following graph −
在图中
V = {a, b, c, d, e}
E = {ab, ac, bd, cd, de}
我们可以在python程序中显示此图，如下所示。
# Filename : example.py
# Copyright : 2020 By Lidihuo
# Author by : www.lidihuo.com
# Date : 2020-08-15
# Create the dictionary with graph elements
graph = { "a" : ["b","c"],
"b" : ["a", "d"],
"c" : ["a", "d"],
"d" : ["e"],
"e" : ["d"]
}
# print the graph
print(graph)
运行结果如下：
{'c': ['a', 'd'], 'a': ['b', 'c'], 'e': ['d'], 'd': ['e'], 'b': ['a', 'd']}
显示图顶点
为了显示图顶点，我们简单地找到图字典的键。我们使用keys()方法。
# Filename : example.py
# Copyright : 2020 By Lidihuo
# Author by : www.lidihuo.com
# Date : 2020-08-15
class graph:
def __init__(self,gdict=None):
if gdict is None:
gdict = []
self.gdict = gdict
# Get the keys of the dictionary
def getVertices(self):
return list(self.gdict.keys())
# Create the dictionary with graph elements
graph_elements = { "a" : ["b","c"],
"b" : ["a", "d"],
"c" : ["a", "d"],
"d" : ["e"],
"e" : ["d"]
}
g = graph(graph_elements)
print(g.getVertices())
运行结果如下：
['d', 'b', 'e', 'c', 'a']
显示图形边缘
查找图的边缘比顶点要难得多，因为我们必须找到在一对顶点之间具有边的一对顶点。因此，我们创建了一个空边列表，然后通过迭代与每个顶点关联的边值。形成一个列表，其中包含从顶点找到的不同边缘组。
# Filename : example.py
# Copyright : 2020 By Lidihuo
# Author by : www.lidihuo.com
# Date : 2020-08-15
class graph:
def __init__(self,gdict=None):
if gdict is None:
gdict = {}
self.gdict = gdict
def edges(self):
return self.findedges()
# Find the distinct list of edges
def findedges(self):
edgename = []
for vrtx in self.gdict:
for nxtvrtx in self.gdict[vrtx]:
if {nxtvrtx, vrtx} not in edgename:
edgename.append({vrtx, nxtvrtx})
return edgename
# Create the dictionary with graph elements
graph_elements = { "a" : ["b","c"],
"b" : ["a", "d"],
"c" : ["a", "d"],
"d" : ["e"],
"e" : ["d"]
}
g = graph(graph_elements)
print(g.edges())
运行结果如下：
[{'b', 'a'}, {'b', 'd'}, {'e', 'd'}, {'a', 'c'}, {'c', 'd'}]
添加一个顶点
直接添加顶点是在图字典中添加另一个键的过程。
# Filename : example.py
# Copyright : 2020 By Lidihuo
# Author by : www.lidihuo.com
# Date : 2020-08-15
class graph:
def __init__(self,gdict=None):
if gdict is None:
gdict = {}
self.gdict = gdict
def getVertices(self):
return list(self.gdict.keys())
# Add the vertex as a key
def addVertex(self, vrtx):
if vrtx not in self.gdict:
self.gdict[vrtx] = []
# Create the dictionary with graph elements
graph_elements = { "a" : ["b","c"],
"b" : ["a", "d"],
"c" : ["a", "d"],
"d" : ["e"],
"e" : ["d"]
}
g = graph(graph_elements)
g.addVertex("f")
print(g.getVertices())
运行结果如下：
['f', 'e', 'b', 'a', 'c','d']
添加边缘
将边缘添加到现有图形涉及将新顶点视为元组，并验证边缘是否已存在。如果没有，则添加边缘。
# Filename : example.py
# Copyright : 2020 By Lidihuo
# Author by : www.lidihuo.com
# Date : 2020-08-15
class graph:
def __init__(self,gdict=None):
if gdict is None:
gdict = {}
self.gdict = gdict
def edges(self):
return self.findedges()
# Add the new edge
def AddEdge(self, edge):
edge = set(edge)
(vrtx1, vrtx2) = tuple(edge)
if vrtx1 in self.gdict:
self.gdict[vrtx1].append(vrtx2)
else:
self.gdict[vrtx1] = [vrtx2]
# List the edge names
def findedges(self):
edgename = []
for vrtx in self.gdict:
for nxtvrtx in self.gdict[vrtx]:
if {nxtvrtx, vrtx} not in edgename:
edgename.append({vrtx, nxtvrtx})
return edgename
# Create the dictionary with graph elements
graph_elements = { "a" : ["b","c"],
"b" : ["a", "d"],
"c" : ["a", "d"],
"d" : ["e"],
"e" : ["d"]
}
g = graph(graph_elements)
g.AddEdge({'a','e'})
g.AddEdge({'a','c'})
print(g.edges())
运行结果如下：
[{'e', 'd'}, {'b', 'a'}, {'b', 'd'}, {'a', 'c'}, {'a', 'e'}, {'c', 'd'}]
