我写了一个代码，查询一个mongo数据库，并将结果写入一个文件。我的代码创建了这个文件并开始写入它成功。但是在多次迭代之后（不确定迭代次数是否固定），我得到了一个PermissionError。
我已经搜索过了，但我只找到了关于第一次尝试时出错的人的答案，因为他们没有权限。我会精确地说，我没有在我的电脑上做任何事情，在执行过程中，所以我真的不明白它是如何发生的。

以下是部分代码：

def query(self, query_date_part, query_actKey_part, filepath):
    empty = True
    print("0.0 %")
    for i in range(len(query_date_part)):
        query = {"dt": query_date_part[i], "actKey": query_actKey_part}
        cursor = self.collection.find(query)
        while cursor.alive:
            try:
                if empty:
                    with open(filepath, 'w') as fp:
                        json.dump(cursor.next(), fp, default=json_util.default)
                        empty = False
                else:
                    append_to_json(filepath, cursor.next())
            except StopIteration:
                print("Stop Iteration")
        print(str(round(float(i+1) / len(query_date_part) * 100, ndigits=2)) + " %")
    return 0

def append_to_json(filepath, data):
    """
    Append data in JSON format to the end of a JSON file.
    NOTE: Assumes file contains a JSON object (like a Python dict) ending in '}'.
    :param filepath: path to file
    :param data: dict to append
    """
    # construct JSON fragment as new file ending
    new_ending = ", " + json.dumps(data, default=json_util.default)[1:-1] + "}\n"
    # edit the file in situ - first open it in read/write mode
    with open(filepath, 'r+') as f:
        f.seek(0, 2)        # move to end of file
        index = f.tell()    # find index of last byte
        # walking back from the end of file, find the index
        # of the original JSON's closing '}'
        while not f.read().startswith('}'):
            index -= 1
            if index == 0:
                raise ValueError("can't find JSON object in {!r}".format(filepath))
            f.seek(index)
        # starting at the original ending } position, write out
        # the new ending
        f.seek(index)
        f.write(new_ending)`

部分输出：

6.75 %
Stop Iteration
6.76 %
Traceback (most recent call last):
    File "C:/Users/username/PycharmProjects/mongodbtk/mquerytk.py", line 237, in <module>
        mdbc.query(split_date(2017,5,6,1,0,2017,5,16,10,0,step=2), {"$in": ["aFeature"]}, 'test.json')
    File "C:/Users/username/PycharmProjects/mongodbtk/mquerytk.py", line 141, in query
        append_to_json(filepath, cursor.next())
    File "C:/Users/username/PycharmProjects/mongodbtk/mquerytk.py", line 212, in append_to_json
        with open(filepath, 'r+') as f:
PermissionError: [Errno 13] Permission denied: 'test.json'
Process finished with exit code 1

**注意：**文件大小在执行过程中会增加。当它崩溃它是大约300莫，我仍然有很多空间在我的硬盘驱动器，但也许文件的大小可以是一个问题？
**配置：**我使用Windows 7，Python 3.6，IDE为PyCharm Community Edition 2016.3.2