Vensim (DDE) + Python

[apix]

Hi everybody,

I need to connect a Python script to Vensim, using the last one as DDE server.
I looked at DDESERV.XLS file in the samples directory of Vensim and learned how VBA functions work.
I found a nice module for Python, able to connect, for example, Python to MS Access (that works as DDE Server). The python script works with Access, but not with Vensim:
The script get connected to Vensim but it can't load any model.

Can you help me?

Many thanks, bye bye.

[Administrator]

Can you post anything for us to take a look at?

[apix]

Of course, you're right, sorry.
Here's my script:

Code: Select all

import win32ui
import dde

s = dde.CreateServer()
s.Create("TestClient")
c = dde.CreateConversation(s)

c.ConnectTo("VENSIM", "System") 
if c.Connected() == 1:
    print "Connection established"

comando = "[SPECIAL>LOADMODEL|C:\Program Files\Vensim\models\sample\EXTRA\ball.mdl]"
c.Exec(comando)

I'm working on a Win XP SP3 machine with Python 2.5.4 and pywin32-207.win32-py2.5.

First I open Vensim without loading any model, then I run the script and I get the message "Connection established".

Thanks for your help!

[Administrator]

And what error message are you getting on "c.Exec(comando)" line?

[apix]

Actually I don't get any error message but Vensim doesn't show (load) any model, as indeed it does with excel+dde.

[Administrator]

Does "c.Exec(comando)" return a value? If yes, what is the value of nResult below?

nResult = c.Exec(comando)

[apix]

nResult = None

[Administrator]

Another question. Is Python similar to C where you need double \\?

What happens if you try
comando = "[SPECIAL>LOADMODEL|C:\\Program Files\\Vensim\\models\\sample\\EXTRA\\ball.mdl]"
c.Exec(comando)

[apix]

Nothing happens, no error messages, no value for nResult.
Strange.

If I use the same code to connect the Python script to a MS Access database, it works:
I can see the database loaded, even if nResult gets value "None".

Code: Select all

import win32ui
import dde

s = dde.CreateServer()
s.Create("TestClient")
c = dde.CreateConversation(s)
c.ConnectTo("MSAccess", "System")

if c.Connected() == 1:
    print "Connection established"
    comando = "[OpenDatabase 'C:\db1.mdb']"
    nResult = c.Exec(comando)
    print nResult

[tomfid]

You might try moving the ball.mdl to a location with a simpler path, as with your mdb example, to see if the problem is an issue with the path (like the space in 'program files').

[Administrator]

Tom is right. It could be that Vensim is stopping at the space so is trying to run
"[SPECIAL>LOADMODEL|C:\Program]"

[tomfid]

In any case, quoting the file path, as in

SPECIAL>LOADMODEL|"C:\Documents and Settings\All Users\Vensim\models\guide\CHAP03\wfinv.mdl"

shouldn't hurt.

I assume that in Python you'd have to escape the \ to \\ and the " to \" or something like that.

Tom

[apix]

Thank you for your advices, but quoting the path and/or simplifying it didn't solve the problems.

But, if I first run the excel sample file and then run the python script, I can get the results of the model.
That means that the scipt actually get connected to vensim and that the request command works fine.

There must be some problems with the execute command as you imagined.

I'll continue doing tests with it, thanks a lot.