Python 从MongoDB（PyMongo）访问集合时出现关键错误

为什么这样做有效：

import pymongo
from selenium import webdriver
import smtplib
import sys
import json

from pymongo import MongoClient
client = MongoClient('localhost', 27017)

db = client.properties
collection = db['capitalpacific']

fromDB = []

if collection.count() != 0:
    for post in collection.find():
        fromDB.append(post)

print(fromDB[0]['url']) 

仅正确打印集合（xxx.com）文档1中的url

但当我这样做时，会出现一个键错误：

for i in range(0, 2):
print(fromDB[i]['url'}

KeyError:“url”

数据库中存储的文档如下所示：

---

{'url'：'xxx.com'，'location'：'oregon'}

keyrerror通常表示字典集合中不存在该键

例如：

>>> mydoc1=dict(url='xxx.com', location='oregon')
>>> mydoc2=dict(wrongkey='yyy.com', location='oregon')
>>> mylist=[]
>>> mylist.append(mydoc1)
>>> mylist.append(mydoc2)
>>> print mylist[0]['url']
xxx.com

>>> for i in range(0, 2):
...     print(mylist[i]['url'])
...
xxx.com
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
KeyError: 'url'
>>>

>>> print mylist
[{'url': 'xxx.com', 'location': 'oregon'}, {'wrongkey': 'yyy.com', 'location': 'oregon'}]