Is there an obvious way to do this in python?

[Bruno Desthuilliers]

H J van Rooyen a écrit :
> Hi,
> 
> I want to write a small system that is transaction based.
> 
> I want to split the GUI front end data entry away from the file handling and
> record keeping.
> 
> Now it seems almost trivially easy using the sockets module to communicate
> between machines on the same LAN, so that I want to do the record keeping on one
> machine.
> 
> I want to keep the "server" machine as simple as possible - just doing record
> keeping on a stimulus response basis - I would prefer it to do one thing at a
> time to completion because this style of operation, though limited in
> performance, keeps a lot of hassles out of life - a transaction has either
> completed, or it has not - recovery scenarios are relatively easy...

IOW, you want a SQL DBMS. May I recommand PostgreSQL ?

> Up to this point, I don't have a problem - my toy system can create a dummy
> transaction, and I can echo it from the "server" machine, with more than one
> "user" machine running - so I think it is feasible to have several tens of "data
> entry terminal" systems running, served by one not very strong machine.
> 
> Now what I would really like to do is to differentiate between the 'User"
> machines, so that some can do a full range of transactions, and others a limited
> range.

Any decent SQL DBMS is able to handle this. It's kind of builtin...

> And I would like to make this flexible, so that it becomes easy to introduce new
> transactions, without having to run around updating the code in all the user
> machines, with the concomitant version number hassles.

Then you want a web front end.

> And I would like to do the whole thing in python

You'll at least need bits of SQL (but SQLAlchemy may hide away most of 
it) and HTML (but there are some python packages that knows how to build 
HTML from declarative Python code).

> - so my question is this - is
> it possible to do the equivalent of dynamic linking? - i.e. if I keep a list of
> what a user is allowed to do

In SQL : GRANT/REVOKE

> - can I somehow send him just the bits he needs to
> do the job, without having to change the static code on his machine?

HTTP/HTML.

> - it seems
> to me that the eval() thingy could possibly do this for me,

Err... I thought you wanted a reasonnably secure system, but I may have 
misunderstood.

> by sending it data
> that makes it do import statements followed by calls to whatever... - will this
> work, or is there a better way?
> 
> Or has all this been done already?

Yes, it's called a web frontend for a SQL DBMS. There's no shortage of 
Python frameworks to do this kind of things.

> - and no I don't want a web server

If you don't want Apache, there are Python-based application servers. 
CherryPy comes to mind.

> and php

Why PHP ?

> and browsers and Java

Why Java ?

> and html or xml... - I want to write something that works
> simply and reliably

We do write SQL-based web apps all day long, and I can tell you they are 
certainly more simple and reliable than whatever eval()-based home-made 
solution we could imagine !-)