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Python - EOF/BOF exception when using GetRows() function (from MDX query)

I wrote this code to retrieve data from a cube:
rs = win32com.client.Dispatch('ADODB.RecordSet')
rs.__init__
conn = win32com.client.Dispatch('ADODB.Connection')
conn.__init__
conn.CommandTimeout=3000
conn.Open(connString)
#Retrieving data
try:
rs.Open(mdxQuery, conn, 1, 3)
except Exception as e:
print("An error occured while trying to retrieve data:")
print(str(e))
sys.exit(1)
try:
t=rs.GetRows()
except Exception as ex:
print(str(ex))
it seems the mdx query is ok, and retrieve some result (I can see it from debug mode)
but when I try to assign the result of GetRows() function to a variable, it fails, with the following message:
ADODB.Field : Either BOF or EOF is True, or the current record has been deleted. Requested operation requires a current record.
It seems to me GetRows() function is not able to handle NULL values. Is there a way to tell that method to skip NULL values or just fill it with blanks, and avoid this error?
Thanks

how to use try and except in python?

I am trying to get the user_id from the sqlite3 database in python and store in in an array. This is what I have tried:
LIST_ARRAY=[]
def start(bot, update):
value = update.message.from_user.id
print("VALUE first: ", value)
try:
for row in connection.execute("SELECT *from userdetails WHERE user_id=?", (value,)):
print(row)
user_id, full_name, address, phone_number, email = row
data = [user_id]
LIST_ARRAY[0] = data[0]
except:
print(LIST_OF_ADMINS)
It doesn't get the value please help me to sort this out.
My data variable doesn't get added in the list array

i cant help you with the database issue but i can answer the question of "How to use try and except in python"
Try and Except are used in python to handle errors when they occur in your code as shown below
x=[0,'It Worked',2]
try:
print(x[4])
except IndexError:
print("Oh No there was an error")
try:
print(x[1])
except IndexError:
print("Oh No there was an error")
so in the example i made above i created an array with 2 ints and a string... I then "TRY" to print the contents in x[4] which do not exist which results in a IndexError... because i told the program to print(x[4]) and the error that i prepared for occurred the "EXCEPT" statement is executed and the code beneath it is also executed
the output of the code is:
'Oh No there was an error'
'It Worked'

Why fetchall always results in `None`?

Here are data in MySQL database：
python3 table：users_info
But when i use fetchall to get all data in tables it always return none!!
I really really dont konw how to fix it,can someone has met this problem?
the followings are the code files.
encapsulation.py
import MySQLdb
class mysql_encapsulation(object):
def __init__(self,host,port,user,passwd,db,charset):
self.host = host
self.port = port
self.user = user
self.passwd = passwd
self.db = db
self.charset = charset
def open(self):
self.conn = MySQLdb.connect(host=self.host,port=self.port,user=self.user,passwd=self.passwd,db=self.db,charset=self.charset)
self.cursor = self.conn.cursor()
def close(self):
self.cursor.close()
self.conn.close()
def operate(self,sql,params):
try:
self.open()
self.cursor.execute(sql,params)
self.conn.commit()
print(' operate ok')
self.close()
except Exception,e:
print(e.message)
self.conn.rollback()
def get_result_set(self,sql,params=[]):
result=None
try:
self.open()
self.cursor.execute(sql,params)
result = self.cursor.fetchall()
self.close()
except Exception,e:
print('error!')
print(e.message)
return result
use.py(problem in this file)
#coding=utf-8
from encapsulation import *
mysql = mysql_encapsulation(port=3306,host='localhost',user='root',passwd='mysql',
db='python3',charset='utf8')
sql='select id,name from users_info where id=3'
result=mysql.get_result_set(sql)
print (result)

The problem happens in this method;
def get_result_set(self,sql,params=[]):
result=None
try:
self.open()
self.cursor.execute(sql,params)
result = self.cursor.fetchall()
self.close()
except Exception,e:
print('error!')
print(e.message)
return result
One of the first 3 lines in the try block (self.open / self.cursor.exec / result = self.cursor.fetch) generate an error, which you are then catching in the except block and (you can see that it prints "error!"). That's why the result always stays in it's default None value. Remove the except block and it will tell you what kind of error occured.
You should almost never catch the bare Exception but instead catch specific kinds of exception and handle each of them correctly, this problem is a prefect example why.
The error in question probably happens because in your SQL query you are selecting id and name, when the columns in your table are actually id and user_name. So your SQL query should be like this;
sql = 'select id, user_name from users_info where id = 3'

Did you check your sql statement? Based on your table your columns are "id", "user_name" and "passwd", but in your sql you are searching for "id" and "name", and "name" isn't a column so that will throw an error. Change your sql to "sql='select id,user_name from users_info where id=3'"

As ruohola already explained in his answer, your exception handler is hiding all the important informations about what really went wrong - FWIW, there's the "Error !" string printed in your screen capture just above the None. The point is: your try/except block is not only useless, it's actually harmful - it prevents some other code up the call stack to even be aware that there was a problem (and eventually solve it), it also prevents you from knowing what went wrong. As a general rule, only catch exception the exact exception that you expect AND can effectively handle at this point in the code - if you can't fix the error at this point, let the exception propagate and let the calling code deal with it. Also, you want to have as few code as possible in your try clause (the only exception being the application's top-level exception handler of course).
This being said, there is indeed a very valid reason for wanting to be warned of exception, which is to make sure you free resources (and eventually rollback a transaction), but then you want 1/ to use a finally clause for resources cleanup (a finally block is always executed, whatever happens) and 2/ for the rollback part, use an except clause but re-raise the exception, ie:
# leave this one out of the try block -
# there's nothing you can do here about a connection error
# so let the calling code deal with it
self.connect()
try:
self.cursor.execute(sql, params)
except Exception as e:
self.connection.rollback()
finally:
# this will ALWAYS be executed (unless `self.connect()` raised
# but then you don't even want to close the connection <g>
self.close()
wrt/ the real cause of your problem, Kurose's answer is certainly the right one.
Also, there are a quite a few other things that are debatable with your "mysql_encapsulation" class (the naming to start with but let ignore this ATM), the main one being to open and close the connection for each query. Opening a database connection has a rather high cost, so you want to keep it opened as long as possible (and eventually reconnect if you get a "2006 mysql has gone away" error).

determine type of exception by psycopg2

I'm using python with psycopg2. the following snippet produces some sort of error, but i'm not able to get any output, so i can't handle the error
cur = conn.cursor()
try:
cur.execute("INSERT INTO mqtt.records(client, id_type, value) VALUES (%(str)s, %(int)s, %(float)s)", (topic[1], switchCase(topic[-1]), msg.payload)
except psycopg2.Error as e:
print(e)
conn.commit()
cur.close()
i'm pretty sure it's some sort of typecast error, but it's not catched by the except psycopg2.Error as e:. if i'm using a general except: to catch any exceptions, it catches. but then i don't know how to get the error-message

using except Exception as e: i got the message 'arguments can't be mixed' which led me to figure that ... VALUES (%(str)s, %(int)s, %(float)s) isnt working.
instead i had to do typecasting on the (str(topic[1]), int(switchCase(topic[-1])), float(msg.payload)) part.
so i basicly missunderstood the docs. shame on me.

Python-mysql: when to explicitly rollback a transaction

Suppose, I have a modifying statement:
cursor = conn.cursor()
# some code
affected_rows1 = cursor.execute(update_statement1, params1)
# some code
conn.commit()
cursor.close()
Should I wrap the block of code with a try ... except and explicitly rollback a transaction when an exception is raised, and which MySQLdb exceptions should I catch to rollback? I used to catch any StandardError in this case, but now I have a hesitation that the block of code would even need an explicit rollback at all.
The following example is slightly more difficult, and I understand that it does require an explicit rollback if the first update statement succeeded. Still, which exceptions should I catch in this case:
cursor = conn.cursor()
# some code
affected_rows1 = cursor.execute(update_statement1, params1)
# some code
affected_rows2 = cursor.execute(update_statement2, params2)
#some code
conn.commit()
cursor.close()

This link shows the various types of Errors that you can catch. MySQLdb.Error is the standard base class from which all other MySQL Errors are derived.
I usually use MySQLdb.Error because it lets you focus on errors relating to MySQLdb itself. By contrast StandardError will catch almost all the exceptions (not something you want if you want better debugging capability). Plus the use of MySQLdb.Error allows you to display the exact error message (MySQL error number and all) so that you can debug it faster.
Coming to the first part of the question, in case of database statements it is (usually) necessary to rollback transactions (if they are supported) in case of error.
The methodology that I follow is to wrap each execute statement in a try except clause (catching MySQLdb.Error) and using rollback if there is an an error before printing the error message and exiting.
However, there is a catch. In MySQLdb the changes that you make to DB are not actually written to the database until you explicilty call commit. So, logically, rollback is not necessary.
As an example,
conn = MySQLdb.connection(db=, host=, passwd=, user=)
cur = conn.cursor()
#Say you have a table X with one entry id = 1 and total = 50
cur.execute("update X set total = 70 where id = 1")
#Actual DB has not yet changed
cur.execute("update X set total = 80 where id = 1")
#Actual DB has still not changed
If you exit the program without commiting, the value in DB will still be 50 because you never called commit().
This is how you would ideally do it:
conn = MySQLdb.connection(db=, host=, passwd=, user=)
cur = conn.cursor()
#Say you have a table X with one entry id = 1 and total = 50
try:
cur.execute("update X set total = 70 where id = 1")
except MySQLdb.Error,e:
print e[0], e[1]
conn.rollback()
cur.close()
conn.close()
#print lengthy error description!!
sys.exit(2)
#Note: Value in table is still 50
#If you do conn.commit() here, value becomes 70 in table too!!
try:
cur.execute("update X set total = 80 where id = 1")
except MySQLdb.Error,e:
print e[0], e[1]
conn.rollback()
cur.close()
conn.close()
#print lengthy error description!!
sys.exit(2)
#Value in DB will be
#a) 50 if you didn't commit anywhere
#b) 70 if you committed after first execute statement
conn.commit()
#Now value in DB is 80!!
cur.close()
conn.close()

IMHO, you should rollback transactions if you continue to use the same connection. Else everything before the error will get commit when you finish the transactions.
For the exception to catch, I always use MySQLdb.Error but I'm not sure that's correct.

Its advised to wrap execute() in a sub. This is how i do it.
def executeSQL(self, stmt):
cursor = self.dbHand.cursor()
if not stmt.endswith(";"):
stmt += ';'
try:
cursor.execute(stmt)
except MySQLdb.Error, e:
self.logger.error("Caught MYSQL exception :%s: while executing stmt :%s:.\n"%(e,stmt))
return False