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Python hide already printed text

I'm creating a simple two-player board game where each player must place pieces on their own boards. What I would like to do is by either:
opening a new terminal window (regardless which OS the program is run on) for both players so that the board is saved within a variable but the other player cannot scroll up to see where they placed their pieces.
clearing the current terminal completely so that neither player could scroll and see the other player's board. I am aware of the unix 'clear' command but it doesn't achieve the effect I'm after and doesn't work with all OS's (though this might be something that I'll have to sacrifice to get a working solution)
I have tried clearing the screen but haven't been able to completely remove all the text. I don't have a preference; whichever method is easier. Also, if it would be easier to use a different method that I haven't thought of, all other suggestions are welcome. Thanks in advance!
EDIT: Other solutions give the appearance that text has been cleared but a user could still scroll up and see the text that was cleared. I'd like a way to remove any way that a user could see this text.
EDIT 2: Please read the other answers and the comments as they provide a lot of information about the topic as a whole. In particular, thanks to #zondo.

Consider using a portable terminal handling library. They abstract away the system specifica of common tasks like erasing the "screen" (i.e. terminal), or placing output at a specific position on the "screen" (again, meaning the text terminal). However, to use such a library effectively, you often have to switch to its style of generating output on the screen instead of naively printing strings.
curses is one such library (based on the C library ncurses) and included in the Python standard library. To get started, be sure to have a look at the curses tutorial in the official Python documentation.

I'd personally just use this.
import os
os.system("cls" if os.name == "nt" else "clear") #"cls" for Windows, otherwise "clear"

I would recomend a simple ANSI escape code to move the cursor position, Cursor Escape Codes, to the start of the board everytime. There is also an ANSI escape code that completly clears the console though, so you can choose.
If you are on windows you must first import colorama a module that makes windows prompt be able to use the ANSI codes as such:
import colorama # OR: from colorama import init
colorama.init() # AND THEN: init()
So if your board has n rows, after the user input for their turn, you move the cursor UP n rows + however many were required for user input, so if you wrote Input row, col: ... then you would go UP n+1, etc...
A simple example:
numLines = 1
print("Hello world!")
print("\033[<{0}>A".format(numLines), "This came AFTER hello world line")

You may not like this, it's a bit higher level than a basic two player board game, but there is always using some sort of GUI.
I personally like tkinter myself.
You don't want the option of people scrolling up to see printed text, but you can't remove what has been printed, that's like asking a printer to remove ink off a page. It's going to stay there.
Research a GUI interface, and try and make the game in that. Otherwise, you could let me take a stab at creating a explanatory piece of code that shows you how to use tkinter. If you do, link me the game you have so I can understand what you want.

Take all input in Python (like UAC)

Is there any way I can create a UAC-like environment in Python? I want to basically lock the workstation without actually using the Windows lock screen. The user should not be able to do anything except, say, type a password to unlock the workstation.

You cannot do this without cooperation with operating system. Whatever you do, Ctrl-Alt-Del will allow the user to circumvent your lock.

The API call you're looking for Win32-wise is a combination of CreateDesktop and SetThreadDesktop.
In terms of the internals of Vista+ desktops, MSDN covers this, as does this blog post. This'll give you the requisite background to know what you're doing.
In terms of making it look like the UAC dialog - well, consent.exe actually takes a screenshot of the desktop and copies it to the background of the new desktop; otherwise, the desktop will be empty.
As the other answerer has pointed out - Ctrl+Alt+Delete will still work. There's no way around that - at least, not without replacing the keyboard driver, anyway.
As to how to do this in Python - it looks like pywin32 implements SetThreadDesktop etc. I'm not sure how compatible it is with Win32; if you find it doesn't work as you need, then you might need a python extension to do it. They're not nearly as hard to write as they sound.

You might be able to get the effect you desire using a GUI toolkit that draws a window that covers the entire screen, then do a global grab of the keyboard events. I'm not sure if it will catch something like ctrl-alt-del on windows, however.
For example, with Tkinter you can create a main window, then call the overrideredirect method to turn off all window decorations (the standard window titlebar and window borders, assuming your window manager has such things). You can query the size of the monitor, then set this window to that size. I'm not sure if this will let you overlay the OSX menubar, though. Finally, you can do a grab which will force all input to a specific window.
How effective this is depends on just how "locked out" you want the user to be. On a *nix/X11 system you can pretty much completely lock them out (so make sure you can remotely log in while testing, or you may have to forcibly reboot if your code has a bug). On windows or OSX the effectiveness might be a little less.

I would try with pygame, because it can lock mouse to itself and thus keep all input to itself, but i wouldn't call this secure without much testing, ctr-alt-del probably escape it, can't try on windows right now.
(not very different of Bryan Oakley's answer, except with pygame)

Formatting Python string output

I'm writing a calculator currently and I'd like to have results displayed in a visually appealing form. The program just has a command line interface for the moment, but I've been trying to find a way to do various things with the results it displays. For example, I'd like to have it display the result in a bigger font size, a different font than system default, and even subscripts and superscripts. From what I could find, the best way to do such things would be if I introduced a GUI and used something like wxPython, and using Unicode code points can only resolve part of the issue. Moreover, for various reasons, I'd just like to have the program in command line for the moment.

I don't think you can accomplish this with the command line, but you might check out curses. I would suggest picking up a GUI for this sort of thing. It's really not too hard to learn and Python's builtin Tkinter is perfectly functional for getting started. There are many good resources for Tkinter. Here are a few I like:
effbot.org
Thinking in Tkinter
An Introduction to Tkinter
WxPython is excellent, but if you are just getting started my suggestion would be to start with Tkinter. Others might disagree...
EDIT
I just remembered running across the console module for Windows. I suspect it won't won't get you what you want, but at least it's out there.

If you're running this on the command line, I'm almost certain that there's nothing you can do to override the font preferences set by the user. In both windows and Linux, the font settings of the command line are user controlled, and I doubt that you can change it without sudo access. Seeing as you're writing a calculator, I don't think a user would want to run it as sudo - I certainly wouldn't want to run something as simple as a calculator with sudo privileges. To require that would make the user think that you are up to something malicious

Using Python to read the screen and controlling keyboard/mouse on OSX

I'm looking for or trying to write a testing suite in Python which will control the mouse/keyboard and watch the screen for changes.
The obvious parts I need are (1) screen watcher, (2) keyboard/mouse control.
The latter is explained here, but what is the best way to go about doing the former on OSX?

I can't think of a smart way to "watch the screen for changes" in any OS nor with any language. On MacOSX, you can take screenshots programmatically at any time, e.g. with code like the one Apple shows at this sample (translating the Objective C into Python + PyObjC if you want), or more simply by executing the external command screencapture -x -T 0 /tmp/zap.png (e.g. via subprocess) and examining the resulting PNG image -- but locating the differences between two successive screenshot is anything but trivial, and the whole approach is time consuming (there's no way that I know to receive notification of generic screen changes, so you need to keep repeating this periodically -- eek!-).
Depending on what exactly you're trying to accomplish, maybe you can get away with something simpler than completely unconstrained "watching screen changes"...?

How to make PowerBuilder UI testing application?

I'm not familiar with PowerBuilder but I have a task to create Automatic UI Test Application for PB. We've decided to do it in Python with pywinauto and iaccesible libraries. The problem is that some UI elements like newly added lists record can not be accesed from it (even inspect32 can't get it).
Any ideas how to reach this elements and make them testable?

I'm experimenting with code for a tool for automating PowerBuilder-based GUIs as well. From what I can see, your best bet would be to use the PowerBuilder Native Interface (PBNI), and call PowerScript code from within your NVO.
If you like, feel free to send me an email (see my profile for my email address), I'd be interested in exchanging ideas about how to do this.

I didn't use PowerBuilder for a while but I guess that the problem that you are trying to solve is similar to the one I am trying to address for people making projects with SCADA systems like Wonderware Intouch.
The problem with such an application is that there is no API to get or set the value of a control. So a pywinauto approach can't work.
I've made a small tool to simulate the user events and to get the results from a screencapture. I am usig PIL and pytesser ORM for the analysis of the screen captures. It is not the easiest way but it works OK.
The tool is open-source and free of charge and can be downloaded from my website (Sorry in french). You just need an account but it's free as well. Just ask.
If you can read french, here is one article about testing Intouch-based applications
Sorry for the self promotion, but I was facing a similar problem with no solution so I've written my own. Anyway, that's free and open-source...

I've seen in AutomatedQa support that they a recipe recommending using msaa and setting some properties on the controls. I do not know if it works.

If you are testing DataWindows (the class is pbdwxxx, e.g. pbdw110) you will have to use a combination of clicking at specific coordinates and sending Tab keys to get to the control you want. Of course you can also send up and down arrow keys to move among rows. The easiest thing to do is to start with a normal control like an SLE and tab into the DataWindow. The problem is that the DataWindow is essentially just an image. There is no control for a given field until you move the focus there by clicking or tabbing. I've also found that the DataWindow's iAccessible interface is a bit strange. If you ask the DataWindow for the object with focus, you don't get the right answer. If you enumerate through all of the children you can find the one that has focus. If you can modify the source I also advise that you set AccessibleName for your DataWindow controls, otherwise you probably won't be able to identify the controls except by position (by DataWindow controls I mean the ones inside the DataWindow, not the DataWindow itself). If it's an MDI application, you may also find it useful to locate the MicroHelp window (class fnhelpxxx, e.g. fnhelp110, find from the main application window) to help determine your current context.
Edited to add:
Sikuli looks very promising for testing PowerBuilder. It works by recognizing objects on the screen from a saved fragment of screenshot. That is, you take a screenshot of the part of the screen you want it to find.