How do you get output parameters from a stored procedure in Python?

Question

I've googled around a bit, but maybe I didn't put the correct magik incantation into the search box.

Does anyone know how to get output parameters from a stored procedure in Python? I'm using pymssql to call a stored procedure, and I'm not sure of the correct syntax to get the output parameter back. I don't think I can use any other db modules since I'm running this from a Linux box to connect to a mssql database on a MS Server.

import pymssql

con = pymssql.connect(host='xxxxx',user='xxxx',password='xxxxx',database='xxxxx')

cur = con.cursor()

query = "EXECUTE blah blah blah"

cur.execute(query)
con.commit()
con.close()

Answer 1

2016 update (callproc support in pymssql 2.x)

pymssql v2.x offers limited support for callproc. It supports OUTPUT parameters using the pymssql.output() parameter syntax. Note, however, that OUTPUT parameters can only be retrieved with callproc if the stored procedure does not also return a result set. That issue is discussed on GitHub here.

For stored procedures that do not return a result set

Given the T-SQL stored procedure

CREATE PROCEDURE [dbo].[myDoubler] 
    @in int = 0, 
    @out int OUTPUT
AS
BEGIN
    SET NOCOUNT ON;
    SELECT @out = @in * 2;
END

the Python code

import pymssql
conn = pymssql.connect(
    host=r'localhost:49242',
    database='myDb',
    autocommit=True
    )
crsr = conn.cursor()

sql = "dbo.myDoubler"
params = (3, pymssql.output(int, 0))
foo = crsr.callproc(sql, params)
print(foo)
conn.close()

produces the following output

(3, 6)

Notice that callproc returns the parameter tuple with the OUTPUT parameter value assigned by the stored procedure (foo[1] in this case).

For stored procedures that return a result set

If the stored procedure returns one or more result sets and also returns output parameters, we need to use an anonymous code block to retrieve the output parameter value(s):

Stored Procedure:

ALTER PROCEDURE [dbo].[myDoubler] 
    @in int = 0, 
    @out int OUTPUT
AS
BEGIN
    SET NOCOUNT ON;
    SELECT @out = @in * 2;
    -- now let's return a result set, too
    SELECT 'foo' AS thing UNION ALL SELECT 'bar' AS thing;
END

Python code:

sql = """\
DECLARE @out_value INT;
EXEC dbo.myDoubler @in = %s, @out = @out_value OUTPUT;
SELECT @out_value AS out_value;
"""
params = (3,)
crsr.execute(sql, params)
rows = crsr.fetchall()
while rows:
    print(rows)
    if crsr.nextset():
        rows = crsr.fetchall()
    else:
        rows = None

Result:

[('foo',), ('bar',)]
[(6,)]

Answer 2

If you cannot or don't want to modify the original procedure and have access to the database you can write a simple wrapper procedure that is callable from python.

For example, if you have a stored procedure like:

CREATE PROC GetNextNumber
   @NextNumber int OUTPUT
AS
...

You could write a wrapper like so which is easily callable from python:

CREATE PROC GetNextNumberWrap
AS
    DECLARE @RNextNumber int
    EXEC GetNextNumber @RNextNumber
    SELECT @RNextNumber
GO

Then you could call it from python like so:

import pymssql
con = pymssql.connect(...)
cur = con.cursor()
cur.execute("EXEC GetNextNumberWrap")
next_num = cur.fetchone()[0]

Answer 3

I'm not a python expert but after a brief perusing of the DB-API 2.0 I believe you should use the "callproc" method of the cursor like this:

cur.callproc('my_stored_proc', (first_param, second_param, an_out_param))

Then you'll have the result in the returned value (of the out param) in the "an_out_param" variable.