python实现在指定文件指定位置插入字符

1. 场景

生产环境需要对大量的json文件进行写操作，在指定节点中插入一个属性。如下:

{
    "dataSources":{
        "test_dataSource_hod":{
            "spec":{
                "dataSchema":{
                    "dataSource":"test_dataSource_hod",
                    "parser":{
                        "type":"string",
                        "parseSpec":{
                            "timestampSpec":{
                                "column":"timestamp",
                                "format":"yyyy-MM-dd HH:mm:ss"
                            },
                            "dimensionsSpec":{
                                "dimensions":[
                                    "method",
                                    "key"
                                ]
                            },
                            "format":"json"
                        }
                    },
                    "granularitySpec":{
                        "type":"uniform",
                        "segmentGranularity":"hour",
                        "queryGranularity":"none"
                    },
                    "metricsSpec":[
                        {
                            "name":"count",
                            "type":"count"
                        },
                        {
                            "name":"call_count",
                            "type":"longSum",
                            "fieldName":"call_count"
                        },
                        {
                            "name":"succ_count",
                            "type":"longSum",
                            "fieldName":"succ_count"
                        },
                        {
                            "name":"fail_count",
                            "type":"longSum",
                            "fieldName":"fail_count"
                        }
                    ]
                },
                "ioConfig":{
                    "type":"realtime"
                },
                "tuningConfig":{
                    "type":"realtime",
                    "maxRowsInMemory":"100000",
                    "intermediatePersistPeriod":"PT10M",
                    "windowPeriod":"PT10M"
                }
            },
            "properties":{
                "task.partitions":"1",
                "task.replicants":"1",
                "topicPattern":"test_topic"
            }
        }
    },
    "properties":{
        "zookeeper.connect":"zookeeper.com:2015",
        "druid.discovery.curator.path":"/druid/discovery",
        "druid.selectors.indexing.serviceName":"druid/overlord",
        "commit.periodMillis":"12500",
        "consumer.numThreads":"1",
        "kafka.zookeeper.connect":"kafkaka.com:2181,kafka.com:2181,kafka.com:2181",
        "kafka.group.id":"test_dataSource_hod_dd"
    }
}

需要在最后的properties节点中添加一个"druidBeam.randomizeTaskId":"true"属性。

2. 思路

大概的思路如下：

1. 扫描文件夹下所有需要更改的文件
2. 在文件中确认需要更改的位置
3. 插入新的字符

我觉得稍微有点难的地方是在确认插入位置的地方。我们知道的是"druid.selectors.indexing.serviceName":"druid/overlord",这个东西肯定在这个节点中，那我只要能找到这个东西，然后在他的后面插入就OK了。
好了，思路已经有了，写代码吧。

#!/usr/bin/python
# coding:utf-8

import os


old_string = '"druid/overlord"'
new_string = ('"druid/overlord",' +
              '\n        ' +
              '"druidBeam.randomizeTaskId":"true",')


def insertrandomproperty(file_name):
    if '.json' in file_name:
        with open(file, 'r') as oldfile:
            content = oldfile.read()
            checkandinsert(content, file)

    else:
        pass


def checkandinsert(content, file):
    if 'druidBeam.randomizeTaskId' not in content:
       # to avoid ^M appear in the new file because of different os
       # we replace \r  with '' 
        new_content = content.replace(old_string, new_string).replace('\r', '')

        with open(file, 'w') as newfile:
            newfile.write(new_content)
    else:
        pass


if __name__ == '__main__':
    files = os.listdir('/home/tranquility/conf/service_bak')
    os.chdir('/home/tranquility/conf/service_bak')
    for file in files:
        insertrandomproperty(file)

就是在内存中更新内容，然后重新写回到文件中。代码只是粗略的表达了思路，可以根据需求继续修改优化。