Trying to dive into Qt big time but haven't done a large project with it yet. Currently using Python, but I've been thinking -- which is really the better language to use in terms of programmer productivity?
In most comparisons between the languages, Python is the obvious answer, because you don't have to mess with memory management and all that.
However, with Qt I'm not so sure.  It provides enough added features to C++ that (from what I can tell) a line of Python code is roughly equal to a line of C++ code most of the time (excluding some additional things like class definitions and structure components).  Qt does nearly all the memory management for you as long as you stick with its classes, and provides equivalents to the nice containers you would find in Python.
I've always preferred statically typed languages, but have gotten on the Python bandwagon for various reasons.  If programmer productivity is similar with C++, however, I may jump back that way for its other benefits -- more efficient code and fewer dependencies for users to install.
Thoughts?
definitely Python. 
Yes, people will say that Python is more productive without a reason. Some of the answers mention that you do not have to recompile. I will give you some more details

Python is one layer of abstraction over C++, so you can think and express your designs with less code. Your program might not run as fast, but sure you express faster in code what you want.
The most common case is when you launch your application, load some files, setup the environment and open a dialog. There you notice that a button is not working or where it should be. Now that is the point where most people close the application, bind one slot here, one signal there... and start the application, load the files, setup... with python you just write the code and fire up the dialog again, not the whole application. I do not know about you, but that type of task is what I do most of the time with Qt
Python gives you something that C++ does not have: introspection. You can explore a running program and pull out information about its components on runtime. Qt gives you partially this. You have that MOC layer where meta properties and meta information can be attached to Qt objects. All parts of a Python program can be introspected. Many people debugging Python code, or trying to understand how it works, are addicted to this for a good reason
Qt programming: More productive in Python or C++?