使用cron作业执行python3文件。 [英] Executing python3 file with a cron job.

问题描述

我在/ home / valence /中有一个python3脚本，可以从Yahoo!获取当天的天气预报（摄氏温度的最高和最低温度值）。天气API。该文件看起来完全像这样：

I have a python3 script located in /home/valence/ that gets the weather forecast for the current day (max and min temperature values in Celsius) from Yahoo! weather API. The file looks exactly like this:

#!/usr/bin/python3
from urllib import request
import json
url="https://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20weather.forecast%20where%20woeid%3D349859%20and%20u='c'&format=json&diagnostics=true&callback="
response=request.urlopen(url)
str_response = response.readall().decode('utf-8')
dic = json.loads(str_response)
dic["query"]["results"]["channel"]["location"]["region"]="R.M."
low=dic["query"]["results"]["channel"]["item"]["forecast"][0]["low"]
high=dic["query"]["results"]["channel"]["item"]["forecast"][0]["high"]
forecast=open("forecast.txt", "w+")
forecast.write("Minima: "+str(low)+" Maxima: "+str(high))
forecast.close()

我执行它时效果很好。它使用正确的值创建或覆盖文件Forecast.txt，但是当我尝试使用cron执行以下cron作业时：

It works fine when I execute it. It creates or overwrites the file forecast.txt with the right values, but when I try to use cron to execute with the following cron job:

* * * * * /home/valence/Get_forecast.py

没有文件Forecast.txt是创建或修改的。

no file forecast.txt is created or modified.

所以我需要知道我做错了什么以及如何按预期进行这项工作。 cron作业并不是要每分钟执行一次（因为一天的预测在一天中仍然保持不变），但是现在我有了这种方式，这样我就可以看到更改而不必等待太多。

So I need to know what I am doing wrong and how to make this work as intended. The cron job is not meant to be executed every minute (because forecast for a day remains the same throughout the day), but for now I have it that way so I can see changes without having to wait much.

注意：我是linux新手（正在使用Lubuntu）

Note: I am new to linux (I am using Lubuntu)

推荐答案

原因使用crontab作业<$ c $时，目录 / home / valence 中没有文件 forecast.txt c> * * * * * /home/valence/Get_forecast.py 是cron不在目录 / home / valence ，然后在程序中以相对路径形式指定了文件 forecast.txt 。因此，将在其他位置创建文件。

The reason why you don't get the file forecast.txt in directory /home/valence when using crontab job * * * * * /home/valence/Get_forecast.py is that the cron don't execute the command in directory /home/valence and you specified the file forecast.txt in relative path form in your program. So the file is created somewhere else.

要获得预期的文件输出，可以使用以下crontab作业：

To get the expected file output, you can use the following crontab job:

* * * * * cd /home/valence && ./Get_forecast.py

这明确地将当前工作目录分配为 / home /价，然后从那里执行脚本。

This explicitly assign the current working directory to be /home/valence, and execute the script from there.

此外，要获得stdout和stderr的输出，添加重定向总是有帮助的

What's more, to get the output from stdout and stderr, add redirection is always helpful when something unexpected happens:

* * * * * cd /home/valence && ./Get_forecast.py > /tmp/forecast.log 2>&1

注意：

前面的两个crontab作业假定Get_forecast.py jexecutable并且已指定shebang。 ./ Get_forecast.py 部分始终可以替换为 python3 Get_forecast.py 或 / usr / bin / python3 Get_forecast.py 更清楚。

The previous two crontab job assumes Get_forecast.py jexecutable and with shebang specified. The ./Get_forecast.py part can always be replaced with python3 Get_forecast.py or /usr/bin/python3 Get_forecast.py to be more clear.

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