Question

I have this python code in Tornado:

if not usr:
    self.lock_tables("write", ['devices_permissions'])
        self.db.execute("INSERT devices_permissions SET user_id=%s, network_id=%s, device_id=%s, perm=%s",
                         usrid, netid, sensid, perm)
        self.unlock_tables();

    else:

      if perm == 0:
        self.lock_tables("write", ['devices_permissions'])
        self.db.execute("DELETE FROM devices_permissions \
                         WHERE user_id=%s AND device_id=%s", usrid, sensid)
        self.unlock_tables();


      else:
        self.lock_tables("write", ['devices_permissions'])
        self.db.execute("UPDATE devices_permissions SET perm=%s \
                         WHERE user_id=%s AND device_id=%s", perm, usrid, sensid)
        self.unlock_tables();

I have a problem with the second if…else statement. My program enter in the first else block, but in the second if…else seems not to work the if perm == 0 statement. I have print the perm variable and its value is 0. So I don’t know where sould be the error.

I want this if…else statement because I want delete from my DB the users that didn’t have anymore a permission on a device.

perm is a variable of value 0 or 1. usr is a list of user. Thank you very much.

EDIT

I change the statement in this way:

# Check whether the user has already priviledges on the device
    self.lock_tables("read", ['devices_permissions'])
    usr = self.db.get("SELECT device_id, user_id FROM devices_permissions \
                              WHERE user_id=%s AND device_id=%s", usrid, sensid)
    self.unlock_tables();

    if not usr:
    self.lock_tables("write", ['devices_permissions'])
        self.db.execute("INSERT devices_permissions SET user_id=%s, network_id=%s, device_id=%s, perm=%s",
                         usrid, netid, sensid, perm)
        self.unlock_tables();

    elif perm == 0:
        self.lock_tables("write", ['devices_permissions'])
        self.db.execute("DELETE FROM devices_permissions \
                         WHERE user_id=%s AND device_id=%s", usrid, sensid)
        self.unlock_tables();          

    else:
        self.lock_tables("write", ['devices_permissions'])
        self.db.execute("UPDATE devices_permissions SET perm=%s \
                         WHERE user_id=%s AND device_id=%s", perm, usrid, sensid)
        self.unlock_tables();

and after some test I think that the program enter always in the if not usr statement, also if the usr list is not empty. What’s the problem?

Answer 1

Could it be that perm is the string zero rather than an integer zero? If so, the test perm == 0 would fail. You can answer this question with a print statement:

print type(perm)

if it prints <type 'str'> then that’s your problem.