python打印语句中的意外没有

Question

I'm trying to print out a list of nodes connected to other nodes so I can view them for debugging some python code revolving around graphs. I'm doing this for practice so I'm setting up nodes/edges/groups myself.

I've tried printing out the connections with my function inside of the myNode class using a for each type loop. But I get different output if I specify the index of the array and call the same method on it.

def print_connections(self):
        for node in self.connections:
            print(node.name, end = " ")

...

for node in nodes:
        node.print_connections()
        print(" ") # so I can have a newline in between groups
print(nodes[1].print_connections())

The for/each has good output, or appears to be good:

2 5 3 0 

which differs from the line with the indexed print:

2 5 3 0 None

Is this expected behavior in python? How can I get around this?

Answer 1

your print_connections(self) doesn't return any value, thus return None , and what you're trying to do is with print(nodes[1].print_connections()) is to print the returned value by nodes[1].print_connections() , which is going to be None , so what you should do instead is just,

for node in nodes:
        node.print_connections()
        print(" ") 
nodes[1].print_connections()