如何在python中使用dict使用boto和Amazon EC2构建多维数组？

Question

I'm attempting to use python and boto to print a list of instances and IPs from Amazon EC2.

I'm used to PHP's nice multidimensional arrays and the similar JSON syntax but I'm having a lot of trouble in python. I tried using AutoVivification as mentioned in What's the best way to initialize a dict of dicts in Python? but am not having luck with access objects in it.

Here is my code:

import sys
import os
import boto
import string
import urllib2
from pprint import pprint
from inspect import getmembers
from datetime import datetime

class AutoVivification(dict):
    """Implementation of perl's autovivification feature."""
    def __getitem__(self, item):
        try:
            return dict.__getitem__(self, item)
        except KeyError:
            value = self[item] = type(self)()
            return value

conn = boto.connect_ec2_endpoint(ec2_url, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY)
tags = conn.get_all_tags()
myInstances = AutoVivification()

for tag in tags:
    if ( tag.res_type == 'instance' and tag.name == 'Name'):
        if( tag.res_id ):
            myInstances[tag.res_id]['myid'] = tag.res_id
            myInstances[tag.res_id]['name'] = tag.value

addrs = conn.get_all_addresses()
for a in addrs:
    if( a.instance_id ):
      myInstances[a.instance_id]['ip'] = a.public_ip

pprint( myInstances )

for i in myInstances:
    print i.name.rjust(25), i.myid

If I do pprint( myInstances ) then I am able to see the multidimensional dict that I have created, but i am not able to access the sub-arrays with i.myid - I get errors like:

AttributeError: 'unicode' object has no attribute 'myid'
AttributeError: 'unicode' object has no attribute 'name'

Doing pprint( myInstances) gives me something like:

{u'i-08148364': {'myid': u'i-18243322', 'name': u'nagios', 'ip': u'1.2.3.4'}}

so I don't understand why I can't access these items.

Answer 1

Your problem is just in how you're trying to access the items:

for i in myInstances:
    # i iterates over the KEYS in myInstances
    print i.name.rjust(25), i.myid

This attempts, for each key in myInstances , to print i.name.rjust(25) and so on. What you want is to access the value of the given keys (and to use the right Python syntax for accessing dictionary elements):

for i in myInstances:
    # i iterates over the KEYS in myInstances
    print myInstances[i]["name"].rjust(25), myInstances[i]["myid"]

Or if you don't need the keys at all, just iterate over the values in the first place:

for i in myInstances.values():
    # i iterates over the VALUES in myInstances
    print i["name"].rjust(25), i["myid"]

Or finally, per request, if you really want to iterate over keys and values at once:

for k, v in myInstances.iteritems():
    print k, v["name"].rjust(25), v["myid"]