[Help] [Newbie] Require help migrating from Perl to Python 2.7 (namespaces)

Sat Dec 22 07:38:11 EST 2012

Am Samstag, 22. Dezember 2012 12:43:54 UTC+1 schrieb Peter Otten:
> wrote:
>>>> > Hello, to all,
>> > 
>> > I hope I can describe me problem correctly.
>> > 
>> > I have written a Project split up to one Main.py and different modules
>> > which are loaded using import and here is also my problem:
>> > 
>> > 1. Main.py executes:
>> > 2. Import modules
>> > 3. One of the Modules is a SqliteDB datastore.
>> > 4. A second module creates an IPC socket.
>> > 5. Here is now my problem :
>> > The IPC Socket should run a sub which is stored ad SqliteDB and
>> > returns all Rows.
>> > 
>> > Is there a elegant way to solve it? except a Queue. Is it possible to
>> > import modules multiple?! 
>>>> If you import a module more than once code on the module level will be 
>> executed the first time only. Subsequent imports will find the ready-to-use 
>> module object in a cache (sys.modules).
>>>> > I'm unsure because the open DB file at another
>> > module.
>> > 
>> > How is this solved in bigger projects?
>>>> If I'm understanding you correctly you have code on the module level that 
>> creates a socket or opens a database. Don't do that!
>> Put the code into functions instead. That will give the flexibility you need 
>> for all sizes of projects. For instance
>>>> socket_stuff.py
>>>> def send_to_socket(rows):
>> socket = ... # open socket
>> for row in rows:
>> # do whatever it takes to serialize the row
>> socket.close()
>>>> database_stuff.py
>>>> def read_table(dbname, tablename):
>> if table not in allowed_table_names:
>> raise ValueError
>> db = sqlite3.connect(dbname)
>> cursor = db.cursor()
>> for row in cursor.execute("select * from %s" % tablename):
>> yield row
>> db.close()
>>>>>> main.py
>>>> import socket_stuff
>> import database_stuff
>>>> if __name__ == "__main__":
>> socket_stuff.send_to_socket(
>> database_stuff.read_table("some_db", "some_table"))

Hello Thanks for that answer:
I think I have to write it a bit larger,
This isn't a real code, but it for better overview:
 main.py
 / / \ \
-------------------------------------------------------------------
Datastore | ModbusClient | DaliBusClient | Advanced Scheduler
--------------------------------------------------------------------
Main.py:
import Datastore
Datastore.startup()
....
(Everything should run in threads) 
Datastore.py
# Opens a SQLite DB
# Contains Queries to serve data for other mods
# Central point for updating / Quering etc.
ModbusClient.py
# Opens TCP connection to Modbus Device
!!! Here it's interesting !!!
This module contains predefined Queries and functions
IF I START A FUNCTION a SQL should be executed in Datastore.py
DaliBusClient.py
#Lamps, etc. Functions. 
# Stored Informations should be kept in Datastore
# Advanced scheduler
I don't know, Python allways looks for me like a one script "File". But there are big projects. like the the "Model of an SQL Server", using coordinators no problems running threads and exchange Data through a Backbone. I have searched a lot, but I havent find anything to write the "core" splited up into modules and geting over the scopes etc.
DO I have anything forgotten?! everything unclear?? :-P