Python API 函数以意外顺序调用

Question

I'm a fullstack developer (mainly php+js) and started to experiment with python. My python knowledge is like 5 days old and I'm facing strange problem with order of code execution. Lets start with the code:

app.py

from flask import Flask, request
from libs.dullapi import Dullapi
from libs.db_manager import DbManager

app = Flask(__name__)
db = DbManager()
dullapi = Dullapi(db)

@app.route('/')
def main():
    return dullapi.hello_world()

@app.route('/begin-interrogation', methods=['POST'])
def newHole():
    return dullapi.newHole(request)

db_manager.py

import sqlite3
class DbManager:
    _conobj: sqlite3.Connection

    def __init__(self) -> None:
        self._conobj = sqlite3.connect('../sol.db', check_same_thread=False)

    def holes(self):
        dbres = self._conobj.execute('SELECT * FROM holes')
        return dbres.fetchall()

    def getConnection(self) -> sqlite3.Connection:
        return self._conobj

    def execParams(self, query: str, params):
        cursor = self._conobj.cursor()
        cursor.execute(query, params)
        self._conobj.commit()

    def end(self) -> None:
        self._conobj.close()

dullapi.py

from flask import Request
from libs.db_manager import DbManager
import time
import uuid

class Dullapi:
    db: DbManager

    def __init__(self, db: DbManager) -> None:
        self.db = db

    def hello_world(self):
        data = self.db.holes()
        self.db.end()
        return {
            "ewhat": 14,
            'holes': data
        }

    def newHole(self, req: Request):
        newHid = uuid.uuid4()
        self.db.execParams('INSERT INTO holes (hole_id, creator_id, created_at) VALUES (:hid, :cid, :cat)', {
            "hid": str(newHid),
            "cid": req.get_json()['uid'],
            "cat": int(time.time())
        })
        self.db.end()

        return {
            'rid': str(newHid),
            'status': 1
        }

And /begin-interrogation endpoint gives me this error sqlite3.ProgrammingError: Cannot operate on a closed database. with traceback indicating error on line where self.db.execParams is called.

This is very simple code - I know, but I did a lot different APIs with "this" idea of database manager class without problem like this - but only in PHP.

Is Python multithreaded like for each function call or somehow calls functions asynchronously?

Answer 1

Like mipadi said, you likely already closed the connection to the database with a different request. What I usually do is to not make a global database connection objcect, but rather initialize a new connection on every request where I need it. Then I save the connection object in a global variable. Flask has the g object for this ( from flask import g ), which is "unique" for every request and can only be used within a request context .

Example function you could use to always get a connection, but reuse open ones:

from flask import g

def get_db():
    if not hasattr(g, "db"):
        g.db = DbManager()

    return g.db

In your case it might make sense to incorporate this into your existing DbManager class:)

For closing connections after every request you might want to look at this .