图表是一组对象通过链接连接的一组对象的图形表示。互连对象由称为顶点的点表示，连接顶点的链接称为边。我们的教程在这里详细描述了与图形相关的各种术语和功能。在本章中，我们将看到如何使用python程序创建图形并向其添加各种数据元素。以下是我们在图表上执行的基本操作。
显示图形顶点
显示图形边缘
添加一个顶点
添加边缘
创建一个图
可以使用python字典数据类型轻松呈现图形。我们将顶点表示为字典的关键字，顶点之间的连接也称为边界，作为字典中的值。
看看下面的图表 -
在上面的图中
V = {a, b, c, d, e}
E = {ab, ac, bd, cd, de}
我们可以在下面的python程序中展示这个图。
# 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)当上面的代码被执行时，它会产生以下结果 -
{'c': ['a', 'd'], 'a': ['b', 'c'], 'e': ['d'], 'd': ['e'], 'b': ['a', 'd']}
显示图形顶点
为了显示图形顶点，我们简单地找到图形字典的关键字。我们使用keys（）方法。
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())当上面的代码被执行时，它会产生以下结果 -
['d', 'b', 'e', 'c', 'a']
显示图形边缘
寻找图形边缘比顶点少一些，因为我们必须找到每对顶点之间的边缘。因此，我们创建一个空边列表，然后迭代与每个顶点关联的边值。一个列表形成了包含从顶点找到的不同组的边。
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())当上面的代码被执行时，它会产生以下结果 -
[{'b', 'a'}, {'b', 'd'}, {'e', 'd'}, {'a', 'c'}, {'c', 'd'}]
添加一个顶点
添加一个顶点是直接向我们添加另一个关键字到图形字典。
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())当上面的代码被执行时，它会产生以下结果 -
['f', 'e', 'b', 'a', 'c','d']
添加边缘
将边添加到现有图涉及将新顶点视为元组并验证边是否已经存在。如果不是，则添加边缘。
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())当上面的代码被执行时，它会产生以下结果 -
[{'e', 'd'}, {'b', 'a'}, {'b', 'd'}, {'a', 'c'}, {'a', 'e'}, {'c', 'd'}]
