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Client-Server framework for python

I'm currently working on a University project that needs to be implemented with a Client - Server model.
I had experiences in the past where I was managing the communication at socket level and that really sucked.
I was wondering if someone could suggest an easy to use python framework that I can use for that purpose.
I don't know what kind of details you may need to answer so I'm just going to describe the project briefly.
Communication should happen over HTTP, possibly HTTPS.
The server does not need to send data back or invoke methods on the clients, it just collects data
Many clients send data concurrently to server, who needs to distinguish the sender, process the data accordingly and put the result in a database.

You can use something like Flask or Django. Both frameworks are fairly easy to implement, Flask is much easier than Django IMO, although Django has a built in authentication layer that you can use, albeit more difficult to implement in a client/server scenario like you need.
I would personally use Flask and JWT (JSON Web Tokens), which will allow you to give a token to each client for authentication with the server, which will also let you differentiate between clients, and you can use HTTPS for your SSL/TLS requirement. It is tons easier to implement this, and although I like django better for what it brings to the table, it is probably overkill to have you learn it for a single assignment.
For Flask with SSL, here is a quick rundown of that.
For JWT with Flask, here is that.
You can use any database system you would like.

If I understood you correctly you can use any web framework in python. For instance, you can use Flask (I use it and I like it). Django is also a popular choice among the python web frameworks. However, you shouldn't be limited to only these two. There are plenty of them out there. Just google for them.
The implementation of the client depends on what kind of communication there will be between the clients and the server - I don't have enough details here. I only know it's unidirectional.
The client can be a browser accessing you web application written in Flask where users send only POST requests to the server. However, even here the communication will bidirectional (the clients need to open the page which means the server sends requests back to the client) and it violates your initial requirement.
Then it can be a specific client written in python sending some particular requests to your server over http/https. For instance, your client can use a requests package to send HTTP requests.

Using django for non http requests

Can I use django to handle non http-requests and responses? I have a django web application serving up webpages, and I would like to use it to also communicate with other devices (hand-held gps sending in status reports and receiving ack) over tcp, but django reports that the requests are "
code 400, message Bad HTTP/0.9 request type".
[28/Sep/2015 15:14:26] code 400, message Bad HTTP/0.9 request type ('[V1.0.0,244565434376396,1,abcd,2015-09-28')
[28/Sep/2015 15:14:26] "[V1.0.0,244565434376396,1,abcd,2015-09-28 14:14:12,1-2,865456543459367,2,T1]" 400 -
The message from the device is sent as text over tcp with no http parameters at all.
I haven't found any information on how to do this with django, but it would make my life easier if it was possible.
Thanks!

Not that I know of.
Django is a web framework, so it's designed around a certain paradigm if not a certain protocol.
The design is heavily informed - if not by HTTP - by the notions of URL, request, a stateless protocol, et cetera.
If the template system and the routing system were taken away you would be left with a glorified ORM and some useless bits of code.
However, unless you are dealing with existing devices with their own protocol, you can use Django to build a RESTful service to successfully exchange information with something other than bipeds in front of a web browser.
This article on Dr. Dobb's is very informative.
Django REST, although by no means necessary, can help you.
If you are really stuck with legacy devices and protocols, you could write an adapter/proxy that would receive your devices' requests and translate them to RESTful calls, if you protocol looks enough like HTTP semantically rather than syntactically (as in, if you just have to translate QUUX aaa:bbb:ccc: to GET xx/yy/zz).
If it does not share the slightest bit of HTTP's semantics, I'd say Django can't help you much.

I second the suggestion that you can better handle non-http with other methods, but I do have a suggestion as to how to structure a Django app that could do it. HTTP processing takes place in middleware and you could just make your app be on the top of that stack and either pre-empt other middlewares by returning the response instead of passing it down the stack or preparing a mock request to pass down to other handlers, grabbing the response on the way back to post-process it for your receiver.
This feels hacky and might require a bunch of un-orthodox tricks but that's how I would approach the problem as stated.

Python library for HTTP support - including Content-Encoding

I have a scraper, which queries different websites. Some of them varyingly use Content-Encoding. And since I'm trying to simulate an AJAX query and need to mimic Mozilla, I need full support. There are multiple HTTP libraries for Python, but neither seems complete:
httplib seems pretty low level, more like a HTTP packet sniffer really.
urllib2 is some sort of elaborate hoax. There are a dozen handlers for various web client functions, but mandatory HTTP features like Content-Encoding appearantly aren't.
mechanize: is nice, already somehwat overkill for my tasks, but only supports CE 'gzip'.
httplib2: sounded most promising, but actually fails on 'deflate' encoding, because of the disparity of raw deflate and zlib streams.
So are there any other options? I can't believe I'm expected to reimplement workarounds for above libraries. And it's not a good idea to distribute patched versions alongside my application, because packagers might remove it again if the according library is available as separate distribution package.
I almost don't dare to say, but the http functions API in PHP is much nicer. And besides Content-Encoding:*, I might somewhen need multipart/form-data too. So, is there a comprehensive 3rd party library for http retrieval?

I would consider either invoking a child process of cURL or using python bindings for libcurl.
From this description cURL seems to support gzip and deflate.

Beautiful Soup might work. Just throwing it out there.

Writing a Python mail server with authentication

I'm trying to write a simple mail server using Python.
I found smtpd that can be used as a simple smtp server, but I don't think it supports any form of authentication.
For pop or imap, I haven't found anything at all yet.
I do know Twisted has some support for both smtp and pop or imap, but I can't find any examples or tutorials about it.
An alternative would be to use Clojure, but I still have the same question:
Which libraries should I use and is there any documentation about them?

Here is an example from Twisted.
And the main page. Follow the link for documentation to find the example and a tutorial.
Edit:
Check the attachment for this ticket for an example IMAP server. Definitely read the thread as it talks about the shortcomings of the example.

A bit late probably but for experimentation you might also want to check pymta which is a pure-python SMTP implementation I'm using for some experiments/testing. It supports SMTP basic auth. Documentation should be at a 'decent' level, check the examples directory and the unit tests-
For anything production-related I'd go for twisted if you don't mind the asynchronous nature.

Making an asynchronous interface appear synchronous to mod_python users

I have a Python-driven web interface powered by Apache 2.2 with mod_python and Python 2.4. I need to make an asynchronous process appear synchronous to users of this web interface.
When users access one module on this website:
An external SOAP interface will be contacted with a unique identifier and will respond with a number N
The external interface will respond asynchronously by contacting a SOAP server on my machine between 1 and 10 times (the number N tells us how many responses we will receive)
I need to somehow aggregate these responses and pass them to the original module which will display the information back to the user. The goal is to make the process appear synchronous to the user.
What is the best way to handle this synchronization issue? Is this something Twisted would be well-suited for?
I am not restricting myself to Python for the solution, though it is preferred because everything else on the server is in Python. I prefer a solution that is both scalable and will take a minimal amount of programming time (though I understand that these attributes are somewhat at odds).

Maybe you can use Orbited to get ajax push with long-lived HTTP connections to your web clients. Orbited is based on Twisted, so I think it makes sense to look at if you already know Twisted. Have a look at this tutorial to get started.