InterfaceError using PyMySQL (database connection closes)

Question

I use PyMySQL library and Flask in my program. My view function accesses the database every time it called. After some calls it breaks and raise InterfaceError(0, '') . All next requests also raise InterfaceError (any db query, specifially).

Traceback (most recent call last):
   (several files of mine and Flask)
  File "/home/maxim/.local/lib/python3.7/site-packages/pymysql/cursors.py", line 170, in execute
    result = self._query(query)
  File "/home/maxim/.local/lib/python3.7/site-packages/pymysql/cursors.py", line 328, in _query
    conn.query(q)
  File "/home/maxim/.local/lib/python3.7/site-packages/pymysql/connections.py", line 516, in query
    self._execute_command(COMMAND.COM_QUERY, sql)
  File "/home/maxim/.local/lib/python3.7/site-packages/pymysql/connections.py", line 750, in _execute_command
    raise err.InterfaceError("(0, '')")
pymysql.err.InterfaceError: (0, '')

I read PyMySQL library code and saw, that this error occures if connection's _sock variable is None (i think it means connection is closed). But why is it happen?

I use one connection object for all view functions (ie it is defined outside functions). Do I do it right or I must make new connection every request? Or I need do something other to get rid of this error?

My code: https://pastebin.com/sy3xKtgB
Full traceback: https://pastebin.com/iTU75FUi

Answer 1

I solved my problem by creating a new connection to db every request.

def get_db():
    return pymysql.connect(
        'ip',
        'user',
        'password',
        'db_name',
        cursorclass=pymysql.cursors.DictCursor
    )

I call this function every request.

from flask import Flask, request
from my_utils import get_db

app = Flask(__name__)
@app.route('/get', methods=['POST'])
def get():
    conn = get_db()
    with conn.cursor() as cur:
        pass