pymysql.err.InterfaceError after some hours of usage

Wed Oct 2 01:11:38 EDT 2019

Hello, i use 'module pymysql' for connectivity in my wsgi scripts. For some reason after some hours of i.e. 'http://superhost.gr/files' i get the following error when the script tries to run:
Do you know why this is happening?!
Error: 500 Internal Server Error
Sorry, the requested URL 'http://superhost.gr/files/' caused an error:
Internal Server Error
Exception:
InterfaceError("(0, '')",)
Traceback:
Traceback (most recent call last):
 File "/usr/lib/python3.6/site-packages/bottle.py", line 862, in _handle
 return route.call(**args)
 File "/usr/lib/python3.6/site-packages/bottle.py", line 1740, in wrapper
 rv = callback(*a, **ka)
 File "/home/nikos/wsgi/files.py", line 143, in displayall
 convert()
 File "/home/nikos/wsgi/files.py", line 93, in convert
 cur.execute('''SELECT file FROM files''')
 File "/usr/lib64/python3.6/site-packages/pymysql/cursors.py", line 170, in execute
 result = self._query(query)
 File "/usr/lib64/python3.6/site-packages/pymysql/cursors.py", line 328, in _query
 conn.query(q)
 File "/usr/lib64/python3.6/site-packages/pymysql/connections.py", line 516, in query
 self._execute_command(COMMAND.COM_QUERY, sql)
 File "/usr/lib64/python3.6/site-packages/pymysql/connections.py", line 750, in _execute_command
 raise err.InterfaceError("(0, '')")
pymysql.err.InterfaceError: (0, '')
I only use this opening statement in the beginning of my scripts.
conn = pymysql.connect( host='localhost', user='user', password='pass', db='counters' )
cur = conn.cursor()
Then i execute insert and update sql statements but i never close the connection. I presume python closes the connection when the script ends. Doesn't it?