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Python vs C++ for CUDA web server?

I am planning on writing some software for a web server that uses machine learning to process large amounts of data. This will be real estate data from a MySQL server. I will be using the CUDA framework from Nvidia with python/caffe or the c++ library. I will be using a Tesla P100. Although python is more widely used for machine learning I presume it is hard to write a server app in python without sacrificing performance. Is this true? Is c++ well supported for machine learning? Will anything be sacrificed by writing a professional server app in python (ex: connecting to MySQL database)?

Python is a language that performs worse than c++ in terms of runtime for several reasons:
First and foremost, Python is a scripting language that runs with an interpreter as opposed to c++ which compiled into machine code before running.
Secondly: python runs in the background a garbage collector system while in c++ the memory management is done manually by the programmer.
In your case, I recommend that you work with Python for several reasons:
Writing in Python in CUDA allows you to compile the code even though it is Python (CUDA provides JIT - Just In Time compiler, as well as a compiler and other effective tools), Which greatly improves performance
Python provides many, rich varied libraries that will help you a lot in the project, especially in the field of machine learning.
The development time and code length will be significantly shorter in Python.
From my experience with working at CUDA in the Python language I recommend you use numba and numbapro libraries, they are comfortable to work with and provide support for many libraries like numpy.
Best of luck.

Both C++ and Python are perfectly reasonable languages for implementing web servers. Python is actually quite common, and there are many frameworks for writing web servers in Python such as flask, bottle, django, etc. Architecturally, I wonder whether you really need the machine learning (which I imagine would be a data processing pipeline) and the web server to be the same process / binary; however, even if you do them in the same server, I suspect that either language would be perfectly reasonable; moreover, if you ever came to the point where you needed to run a piece of computation in C++ for performance, using SWIG to call C++ from Python or using some form of message passing from Python to a C++ helper process (such as via gRPC) are options.

COMException accessing WMP from Plex Plugin (using Python for .NET)

My Goal
I'm trying to create a plugin for Plex Media Server (PMS) that will interface with WMP (Windows Media Player) to get metadata about Windows media library items.
The Setup
PMS uses Python 2.7 as its primary script host. Plex Plugins are
written in Python, though they operate in a sandboxed capacity. Unfortunately there's sad little documentation on what exactly the boundaries are on this sandboxed functionality.
I decided to use Python for .NET to access the Windows SDK to interface with WMPLib.
Python for .NET (http://pythonnet.github.io/) is a Python
library used to access functionality from .NET assemblies from within
the Python runtime.
I created a .NET assembly to access WMPLib, which
is a part of the Windows SDK designed to programmatically access the
functionality of WMP. WMPLib is basically a COM Interop wrapper for
.NET targeting wmp.dll.
What's Working?
The whole chain from Python on through the COM-based WMP access is working. If I fire up the embedded Plex Script Host that comes with Plex Media Server (a version of Python 2.7), I can readily access data from WMP. That means that the following links in the chain are all working:
Python is loading Python for .NET
Python for .NET is loading my .NET assembly
My .NET assembly is loading WMPLib (Interop.WMPLib.dll, a .NET assembly for COM Interop)
WMPLib is successfully opening and utilizing wmp.dll (accessed from C:\Windows\System32)
What's Not Working?
Activating the COM Interop part of this chain is not working from within the sandboxed Plex plugin. Again, this plugin is written in standard Python, but something is subtly different about the Python execution environment once the sandboxing code has run. I get the following exception when running the WMP access code from within the plugin:
COMException: Exception from HRESULT: 0xC00D1327
at WMPLib.IWMPPlayer4.get_mediaCollection()
In this scenario I know that Python for .NET is working, because I've already loaded and accessed other things from my .NET assembly at this point.
C:\Windows\System32 is at the front of PATH variable. I'm assuming that COM dlls should be located via the PATH environment variable (This seems to say so), but I'm not entirely certain of that. How a COM assembly should be located in this unique scenario (Python accessing .NET accessing COM) is one of the biggest unknowns for me.
The Questions
How might the Plex plugin sandbox be changing the Python execution environment such that accessing the COM assembly is no longer working?
How should the COM assembly be located and accessed by the environment in this case?
Does it require specific permissions that the Plex sandbox may have locked down?
Maybe I should at least win some kind of prize for arriving at a question that intersects so many different technologies in a uniquely confusing way...
Edit 1
I've ruled out any .NET related issues entirely, thanks to #Paulo's suggestion below. I'm now doing all interop with WMPLib through the comtypes Python library. Now I'm getting the following error:
COMError: (-1072884953, None, (None, None, None, 0, None))
Though -1072884953 is a different error code, a little digging around makes it appear that this error is associated with (maybe equivalent to?) the same error that I was getting through .NET interop (this post makes it appear so).
So now the facts that I'm stuck with are these:
wmp.dll is loading in all cases (which #Paulo helped me to figure
out below).
When the code accessing WMP is run outside the Plex sandbox environment, library items can be accessed from WMP just fine.
When the code accessing WMP is run inside the Plex sandbox environment, library items cannot be accessed from WMP.
The error code that I get (whether from .NET or Python based COM interop is NS_E_CURL_INVALIDPATH: The URL contains a path that is not valid. This error appears to be involved with attempted playback in most cases.
This is odd because I've never gotten as far as playback in my scenario... I'm only attempting to call wmp.mediaCollection
So the Plex sandbox truly seems to be key in this scenario. Any further ideas?
Edit 2
Minimally, this is the code that it takes to fail:
from comtypes.client import CreateObject
wmp = CreateObject("{6BF52A52-394A-11d3-B153-00C04F79FAA6}")
collection = wmp.mediaCollection
That collection = wmp.mediaCollection is where the error happens.
So there really aren't any parameters being passed in that could be causing the failure. To reiterate, this code runs fine in the general Python 2.7 context. It only fails within the Plex plugin sandbox. I don't know how to get details on how the Plex sandbox may be changing the execution environment. I'd imagine my answer lies in that direction.

Let me get this straight, and correct me if I'm wrong:
You have a running instance of Python 2.7, Plex Media Server
You're using a library, Python for .NET, to load a .NET into your process
You're loading WMPLib, an imported COM interop assembly, in .NET to use the Windows Media Player library through Python for .NET
Let's clear this out:
0xC00D1327 is NS_E_CURL_INVALIDPATH:
The URL contains a path that is not valid.
It seems like a legitimate object error, not a COM error.
The DLL search order has little to do with it, since wmp.dll is registered with a full path under InProcServer32 registry keys for each provided class, and that's what ultimately matters.
In fact and as you stated, if you've reached this point, it's clearly not a problem about loading .NET assemblies or COM not finding a DLL.
Now, to the questions:
Since the error seems legit, you might not have access to the media collection (Internet zone?), or WMP is not correctly registered/installed, or some codec is missing or not correctly registered/installed, etc.
What are you loading into WMP? Try with basic things, such as local .WAV, .MP3, .AVI and .MPG files, then try more advanced formats e.g. MPEG4-encoded videos, or maybe remote locations.
You should attempt a more direct approach, although I can't really vouch which is better: win32com (part of pywin32) or comtypes.
It was a long while ago since I've looked at them, so take this with a grain of salt: with comtypes, you're able to use your COM objects much like regular Python objects with properties and methods, while win32com seems more inclined to do things by runtime name dispatching.
At least you'll be punching something you really have to put up with (Python) instead of loading .NET for something that doesn't even require it (WMP).
I don't know what that sandboxing is about, but my guess is that it's a Python-only sandbox, not something that restricts usage of the operating system.
EDIT: Are you providing a filename (e.g. C:\path\to\file.mp4) where a URL is expected (file:///C:/path/to/file.mp4), or vice-versa? I guess you must show the failing code and what values are being provided.

Integrating Jython Cpython

I am about to begin a project where I will likely use PyQt or Pyside.
I will need to interface with a buggy 3rd party piece of server software that provides C++ and Java APIs. The Java APIs are a lot easier to use because you get Exceptions where with the C++ libraries you get segfaults. Also, the Python bindings to the Java APIs are automatic with Jython whereas the Python bindings for the C++ APIs don't exist.
So, how would a CPython PyQt client application be able to communicate with these Java APIs? How would you go about it?
Would you have another separate Java process on the client that serializes / pickles objects and communicates with the PyQt process over a socket?
I don't want to re-invent the wheel... is there some sort of standard interface for these types of things? Some technology I should look into? RPC, Corba, etc?
Thanks,
~Eric

If you want to maintain complete isolation and increase your robustness (the 3rd party library going down and not taking your client, and if it's buggy I would recommend that) then perhaps something like CORBA is the way forwards. Don't forget that Java comes with a CORBA implementation as standard, so you just need to generate your C proxy from the IDL.
Swig may be of interest if you want to run stuff in-process. It simplifies the binding of components in different languages. Note in particular that it generates bindings for Python and Java.

If the criteria is not reinventing the wheel, there is the SimpleXMLRPCServer and xmlrpclib modules available in the standard library. They should work in Jython too.

python _+ django, is it compiled code?

Just looking into python from a .net background.
Is python compiled like .net?
If yes, can it be obfuscated and is it more or less secure than .net compiled code that is obfuscated?
does pretty much every web host (unix) support django and python?

There are many implementations of the Python language; the three that are certainly solid, mature and complete enough for production use are CPython, IronPython, and Jython. All of them are typically compiled to some form of bytecode, also known as intermediate code. The compilation from source to bytecode may take place as and when needed, but you can also do it in advance if you prefer; however Google App Engine, which lets you run small Python web apps, including Django, for free, as one of its limitations requires you to upload source and not compiled code (I know of no other host imposing the same limitation, but then I know of none giving you so many resources for free in exchange;-).
You might be most at home with IronPython, which is a Microsoft product (albeit, I believe, the first Microsoft product to be entirely open-source): in that case you can be certain that it is "compiled like .net", because it is (part of) .net (more precisely, .net and silverlight). Therefore it cannot be neither more nor less obfuscated and/or secure than .net (meaning, any other .net language).
Jython works on JVM, the Java Virtual Machine, much like IronPython works on Microsoft's Common Language Runtime, aka CLR. CPython has its own dedicated virtual machine.
For completeness, other implementations (not yet recommended for production use) include pypy, a highly flexible implementation that supports many possible back-ends (including but not limited to .net); unladen swallow, focused on evolving CPython to make it faster; pynie, a Python compiler to the Parrot virtual machine; wpython, a reimplementation based on "wordcode" instead of "bytecode"; and no doubt many, many others.
CPython, IronPython, Jython and pypy can all run Django (other implementations might also be complete enough for that, but I'm not certain).

I don't know about the security part but.
Python is interpreted. Like PHP. (It's turned into bytecode which CPython reads)
Django is just a framework on top of Python.
Python can be compiled.
And no not all hosts support python + django.

You shouldn't have to worry about obfuscating your code, specially since it's going to run on your server.
You are not supposed to put your code in a public directory anyway. The right thing to do with django (as oposed to PHP) is to make the code accessible by the webserver, but not by the public.
And if your server's security has been breached, then you have other things to worry about...

Obfuscation is false security. And the only thing worse than no security is false security. Why would you obfuscate a web app anyways?
Python is compiled to bytecode and run on a virtual machine, but usually distributed as source code.
Unless you really plan to run your webapp on "pretty much every web host" that question doesn't matter. There are many good hosts that support python and django.

Code obfuscation in .NET are mostly a question of changing variable names to make it harder to understand the disassembled code. Yes, you can do those techniques with CPython too.
Now, why ever you would want to is another question completely. It doesn't actually provide you with any security, and does not prevent anybody from stealing your software.

The Python is interpreted language. But you can compile the python program into a Unix executable using Freeze.

What's the best way to use web services in python?

I have a medium sized application that runs as a .net web-service which I do not control,
and I want to create a loose pythonic API above it to enable easy scripting.
I wanted to know what is the best/most practical solution for using web-services in python.
Edit:
I need to consume a complex soap WS
and I have no control over it.

If I have to expose APIs, I prefer doing it as JSON. Python has excellent support for JSON objects (JSON Objects are infact python dictionaries)

Jython and IronPython give access to great Java & .NET SOAP libraries.
If you need CPython, ZSI has been flaky for me, but it could be possible to use a tool like Robin to wrap a good C++ SOAP library such as gSOAP or Apache Axis C++

Most of the packages on python that a SOAP service through them can be called works on python 2.x, but had problems on Python 3.x
The best fit for python 3.x that I've found is suds-jurko