Error from concurrently reading from MYSQL database

I have a flask program. On the get method for ‘/’ route, python code accesses the MYSQL database with the following

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<code>""" returns cash of current user """
def returncash(argdb):
argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
row = argdb.fetchall()
return row[0]['cash']
</code>
<code>""" returns cash of current user """ def returncash(argdb): argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],)) row = argdb.fetchall() return row[0]['cash'] </code>
""" returns cash of current user """
def returncash(argdb):
    argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
    row = argdb.fetchall()

    return row[0]['cash']

This works most of the time. However if in my browser I reload the page twice quickly on the ‘/’ route, the program hangs. I’ve narrowed it down to this line

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<code>argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
</code>
<code>argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],)) </code>
argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))

Seems like its trying to access the same records at the same time and freezing? There are no error messages, it just never gets to the next line. If I hit refresh a couple more times I get the following error

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<code>ERROR in app: Exception on / [GET]
Traceback (most recent call last):
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 1473, in wsgi_app
response = self.full_dispatch_request()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 882, in full_dispatch_request
rv = self.handle_user_exception(e)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 880, in full_dispatch_request
rv = self.dispatch_request()
^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 865, in dispatch_request
return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) # type: ignore[no-any-return]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePluslandf.py", line 12, in innerFunction
return f(*args, **kwargs)
^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusapp.py", line 31, in index
cash = func.returncash(db)
^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusfunc.py", line 37, in returncash
argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorcursor.py", line 551, in execute
self._handle_result(self._connection.cmd_query(stmt))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 490, in cmd_query
result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 404, in _handle_result
columns[i] = self._protocol.parse_column(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorprotocol.py", line 239, in parse_column
(packet, _) = utils.read_lc_string(packet) # db
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorutils.py", line 199, in read_lc_string
if buf[0] == 251: # xfb
~~~^^^
IndexError: bytearray index out of range
</code>
<code>ERROR in app: Exception on / [GET] Traceback (most recent call last): File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 1473, in wsgi_app response = self.full_dispatch_request() ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 882, in full_dispatch_request rv = self.handle_user_exception(e) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 880, in full_dispatch_request rv = self.dispatch_request() ^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 865, in dispatch_request return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) # type: ignore[no-any-return] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePluslandf.py", line 12, in innerFunction return f(*args, **kwargs) ^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusapp.py", line 31, in index cash = func.returncash(db) ^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusfunc.py", line 37, in returncash argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],)) File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorcursor.py", line 551, in execute self._handle_result(self._connection.cmd_query(stmt)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 490, in cmd_query result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 404, in _handle_result columns[i] = self._protocol.parse_column( ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorprotocol.py", line 239, in parse_column (packet, _) = utils.read_lc_string(packet) # db ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorutils.py", line 199, in read_lc_string if buf[0] == 251: # xfb ~~~^^^ IndexError: bytearray index out of range </code>
ERROR in app: Exception on / [GET]
Traceback (most recent call last):
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 1473, in wsgi_app
    response = self.full_dispatch_request()
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 882, in full_dispatch_request
    rv = self.handle_user_exception(e)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 880, in full_dispatch_request
    rv = self.dispatch_request()
         ^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 865, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)  # type: ignore[no-any-return]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePluslandf.py", line 12, in innerFunction
    return f(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusapp.py", line 31, in index
    cash = func.returncash(db)
           ^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusfunc.py", line 37, in returncash
    argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorcursor.py", line 551, in execute
    self._handle_result(self._connection.cmd_query(stmt))
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 490, in cmd_query
    result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query))
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 404, in _handle_result
    columns[i] = self._protocol.parse_column(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorprotocol.py", line 239, in parse_column
    (packet, _) = utils.read_lc_string(packet)  # db
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorutils.py", line 199, in read_lc_string
    if buf[0] == 251:  # xfb
       ~~~^^^
IndexError: bytearray index out of range

Not too sure what I can do to resolve this. Any help is appreciated! Sorry I am pretty new to programming, hope this all makes sense

I tried adding a lock table to the record on the read, as I thought maybe that was what was causing the issue

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<code>""" returns cash of current user """
def returncash(argdb):
argdb.execute("LOCK TABLES fin_users READ")
argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
row = argdb.fetchall()
argdb.execute("UNLOCK TABLES")
return row[0]['cash']
</code>
<code>""" returns cash of current user """ def returncash(argdb): argdb.execute("LOCK TABLES fin_users READ") argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],)) row = argdb.fetchall() argdb.execute("UNLOCK TABLES") return row[0]['cash'] </code>
""" returns cash of current user """
def returncash(argdb):

    argdb.execute("LOCK TABLES fin_users READ")
    argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
    row = argdb.fetchall()
    argdb.execute("UNLOCK TABLES")

    return row[0]['cash']

but I got the following error

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<code>"GET / HTTP/1.1" 500 -
[2024-05-21 14:25:39,567] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 1473, in wsgi_app
response = self.full_dispatch_request()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 882, in full_dispatch_request
rv = self.handle_user_exception(e)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 880, in full_dispatch_request
rv = self.dispatch_request()
^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 865, in dispatch_request
return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) # type: ignore[no-any-return]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePluslandf.py", line 12, in innerFunction
return f(*args, **kwargs)
^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusapp.py", line 31, in index
cash = func.returncash(db)
^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusfunc.py", line 37, in returncash
argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorcursor.py", line 551, in execute
self._handle_result(self._connection.cmd_query(stmt))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 490, in cmd_query
result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 384, in _handle_result
elif packet[4] == 0:
~~~~~~^^^
IndexError: bytearray index out of range
</code>
<code>"GET / HTTP/1.1" 500 - [2024-05-21 14:25:39,567] ERROR in app: Exception on / [GET] Traceback (most recent call last): File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 1473, in wsgi_app response = self.full_dispatch_request() ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 882, in full_dispatch_request rv = self.handle_user_exception(e) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 880, in full_dispatch_request rv = self.dispatch_request() ^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 865, in dispatch_request return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) # type: ignore[no-any-return] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePluslandf.py", line 12, in innerFunction return f(*args, **kwargs) ^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusapp.py", line 31, in index cash = func.returncash(db) ^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusfunc.py", line 37, in returncash argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],)) File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorcursor.py", line 551, in execute self._handle_result(self._connection.cmd_query(stmt)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 490, in cmd_query result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 384, in _handle_result elif packet[4] == 0: ~~~~~~^^^ IndexError: bytearray index out of range </code>
"GET / HTTP/1.1" 500 -
[2024-05-21 14:25:39,567] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 1473, in wsgi_app
    response = self.full_dispatch_request()
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 882, in full_dispatch_request
    rv = self.handle_user_exception(e)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 880, in full_dispatch_request
    rv = self.dispatch_request()
         ^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesflaskapp.py", line 865, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)  # type: ignore[no-any-return]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePluslandf.py", line 12, in innerFunction
    return f(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusapp.py", line 31, in index
    cash = func.returncash(db)
           ^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusfunc.py", line 37, in returncash
    argdb.execute("SELECT cash FROM fin_users WHERE id = %s", (session['user_id'],))
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorcursor.py", line 551, in execute
    self._handle_result(self._connection.cmd_query(stmt))
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 490, in cmd_query
    result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query))
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:myProgramsfinancePlusvenvLibsite-packagesmysqlconnectorconnection.py", line 384, in _handle_result
    elif packet[4] == 0:
         ~~~~~~^^^
IndexError: bytearray index out of range

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