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

[prilisauer at googlemail.com]

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):
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>     socket = ... # open socket
> 
>     for row in rows:
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>         # 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()
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>     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