Python "If max number of steps is exceeded, break the loop"

Question

我正在编写一个（非常复杂且不雅）Python 代码以通过蛮力对图形进行 3 色着色，并且在我的主要代码块中我试图包含一个声明说"if the max number of runs through the loop exceeds (some arbitrary number), break out of the first (while a in range(0,len(vertices))) loop"。

a = 0
steps = 0   
while a in range(0,len(vertices)):
    for j in newdict:
        steps+=1      #count number of times it goes through the loop
        print(steps)
        if a>=len(vertices) or steps>=100000:
            break     #this is where my error is occurring

        i = vertices[a]
        if dict1[i[0]]==dict1[i[1]] and (list(dict1.values()))!=j:   #if the adjacent vertices are the same color and we have not cycled back to our original dict1,
            dict1[i[1]]=colors[dict1[i[1]]+1]   #change color of the second vertex
            a = 0    #after a vertex is changed colors, I don't want it to keep going: I want the code to stop and reexamine from the top with this new value
            newdict.append(list(dict1.values()))   #running list of all previous dictionaries (attempted colorings): if our dictionary ever cycles through to something it already was, try again
            check = all(dict1[i[0]] != dict1[i[1]] for i in vertices)  # check all adjacent vertices are different colors
            if not check:
                continue
            elif check:
                break  #at any point throughout the code, if the graph is colorable, break the loop and jump to end instead of continuing to color
        elif dict1[i[0]]==dict1[i[1]]:  #if we do eventally cycle back to our original dict1, now we'll try changing the first vertex color
            dict1[i[0]] = colors[dict1[i[0]] + 1]
            a = 0
            newdict.append(list(dict1.values()))
            check = all(dict1[i[0]] != dict1[i[1]] for i in vertices)  # check all adjacent vertices are different colors
            if not check:
                continue
            elif check:
                break  #at any point throughout the code, if the graph is colorable, break the loop and jump to end instead of continuing to color
        else:
            a+=1

但是，我发现即使经过了超过 100000 步（我在打印步数时可以看到），循环也不会中断并变成无限循环，并且步数继续超过 100000。我应该包括另一个循环，

while steps < 100000:

而不是只在我的第一个循环中添加另一个条件？我是犯了语法错误还是我的代码有更深层次的问题？

（完整代码可用 here。）

Answer 1

你有两个循环

while a in range(0,len(vertices)): # Loop 1
    for j in newdict: # Loop 2
        steps+=1      #count number of times it goes through the loop
        print(steps)
        if a>=len(vertices) or steps>=100000:
            break     #this is where my error is occurring

所以当你 break 时，它打破了内部循环，即 for j in newdict: 你必须向 break 循环添加另一个条件 while

Answer 2

向 while 语句添加另一个条件，然后在中断之前设置此条件。

max = False
while a in range(0,len(vertices)) and not max:
...
    for j in newdict:
        ...
        if a>=len(vertices) or steps>=100000:
            max = True
            break     #this is where my error is occurring

Python "If max number of steps is exceeded, break the loop"

Python "If max number of steps is exceeded, break the loop"

python

for-loop

while-loop

graph-coloring