Python graph traversal and use of weak references

The following code is very helpful in the [python standard library:

def all_nodes(self):        yield self        n = self.other        while n and n.name != self.name:            yield n            n = n.other        if n is self:            yield n        return

Yield at the beginning and end of the cycle graph is returned only once, as the starting point and ending point of the cycle graph, and n as the potential node of the graph. The next node is returned in each next call.

With this iterator, you can easily print the structure of the plot:

 def __str__(self):        return '->'.join((n.name for n in self.all_nodes()))

 

Graph:one->two->three->one

 

To implement a graph structure, you must use the weak references in python,

Let's take a look at the code of adding the next node to the standard graph structure:

 def set_next(self, other):        print '%s.next %r' % ( self.name, other)        self.other = other

 

After binding, add a reference to the next node in the attribute field.

 c.__dict__{'other': <Graph at 0xb7507e4c name=2>, 'name': '1'}

 

Therefore, even if you manually call a = None, B = None, c = None, the object will not be deleted.

Garbage:[<Graph at 0xb739856c name=one>, <Graph at 0xb739866c name=two>, <Graph at 0xb739868c name=three>, {'name': 'one', 'other': <Graph at 0xb739866c name=two>}, {'name': 'two', 'other': <Graph at 0xb739868c name=three>}, {'name': 'three', 'other': <Graph at 0xb739856c name=one>}]

Weak references refer to "referencing an object without increasing the pointer count of the referenced object"

You can use c = weekref. ref (k, func)

To specify the referenced object and the Action func after the object is deleted.

When calling, use c () to reference k

However, in the previous example, we need a "proxy object" to proxy the referenced object, so that the set_next function can be used as the variable other with the normal variable.

def set_next(self, other):        if other is not None:            if self in other.all_nodes():                other = weakref.proxy(other)        super(WeakGraph, self).set_next(other)        return

This avoids the use of other () to reference an other object ~