在web.py中打开和关闭文件的位置

Question

A data file was getting corrupted when I terminated the program and realised that it was never properly closed.

It is quite critical that it does not get corrupted. So I added a statement to close the file.

Now, it seems like the file gets opened twice and then closed. That's one operation too many. There are of course many read-write operations in-between but it should only open and close the files once.

Here is what I have done to the standarize web.py template:

import web
import pandas as pd

store = pd.HDFStore('data_file.h5')

urls = (
    '/', 'index'
)

class index:
    def __init__(self):
        self.__df = store['df']
    def GET(self):
        # several read-write, and modify operations on self.__df
        return "Hello, world!"

if __name__ == "__main__":
    try:
        app = web.application(urls, globals())
        app.run()
    finally:
        store.close()

Now, if I move the line which opens the store down inside the try statement at the bottom, it complains since it compiles the class but I can't find the variable store .

I tried initialising store with None at the top but it didn't work either. Then I tried putting that line up at the top in the function and calling it from the bottom, however, that didn't bring it into scope.

I was thinking of making it a global variable, which would probably do the trick, is that the right approach?

Answer 1

See web.py running twice . As mentioned there, avoid using globals as they don't do what you think they do... app.py runs twice, once on startup and a second time within web.appplication(urls, globals()) . If you set autoreload=False in web.applications() call, it won't load the file twice.

Another solution is to attach your store to web.config , which is globally available.

if __name__ == "__main__":
    try:
        web.config.store = pd.HDFStore('data_file.h5')
        app = web.application(urls, globals())
        app.run()
    finally:
        web.config.store.close()

...and reference that global in your __init__

class index:
    def __init__(self):
        self.__df = web.config.store['df']