当所有元素都被迭代时，pymongo 游标会发生什么？答案

【问题标题】：What happens to a pymongo cursor when all its elements have been iterated?当所有元素都被迭代时，pymongo 游标会发生什么？
【发布时间】：2015-11-13 01:20:26
【问题描述】：

我想使用pymongo 从我的数据库中获取一组条目。它似乎返回了一个“光标”。我不知道那是什么。

    all_nodes = pymongo.MongoClient("mongodb://localhost")["provemath"]["nodes"].find(None)

    print('ALL NODES')
    for node in all_nodes:
        print(node)

    print('STILL NODES')
    for node in all_nodes:
        print(node)

有输出：

ALL NODES
{'_notes': [], '_examples': [], '_type': 'definition', '_plural': None, '_counterexamples': [], '_intuitions': [], '_id': 'unique', '_importance': 4, '_name': 'unique', '_dependencies': [], '_description': 'An occurence of a property is __unique__ if the property occurs exactly $1$ time.'}
{'_notes': ['Vertices are often drawn as a dot.  They are also called *nodes*.'], '_examples': [], '_type': 'definition', '_plural': '__vertices__', '_counterexamples': [], '_intuitions': [], '_id': 'vertex', '_importance': 4, '_name': 'vertex', '_dependencies': ['unique'], '_description': 'A __vertex__ is a fundamental unit used to create graphs.'}
{'_notes': ['It is possible that $a=b$.'], '_examples': [], '_type': 'definition', '_plural': None, '_counterexamples': [], '_intuitions': ['Edges are usually drawn as a line or curve connecting two vertices.  In the case that $a=b$, the edge is drawn as a small loop that connects $a$ to itself.'], '_id': 'edge', '_importance': 4, '_name': 'edge', '_dependencies': ['unique', 'vertex'], '_description': 'An __edge__ is a set ${a,b}$ where $a$ and $b$ are vertices.'}
{'_notes': [], '_examples': [], '_type': 'definition', '_plural': None, '_counterexamples': [], '_intuitions': [], '_id': 'loop', '_importance': 4, '_name': 'loop', '_dependencies': [], '_description': 'A __loop__ is an edge $e = {a,a} = {a}$.'}
STILL NODES

游标只能用于一种用途吗？（或者发生了其他事情？）如果我想要常规的数组行为，我将如何获得它？

【问题讨论】：

标签： python-3.x pymongo

【解决方案1】：

是的。光标只适用于一种用途。如mongodb manual中所述

默认情况下，服务器会在 10 点后自动关闭光标不活动的分钟数或客户端是否已用尽光标。

为了让你输出为 python 列表使用

node_list = all_nodes[:]

或

node_list = [node for node in all_nodes]

另见this question

【讨论】：