Debugging python in Atom?
The best debugger I've been able to find for Atom is this: https://atom.io/packages/python-debugger, but it doesn't (from what I can tell) allow you to watch variables. You can step through code and type in the name of the variable you're trying to observe and the plugin will print the variable's value to the console. I think it's just a fancy UI for the pdb debugger tool in Python. If you want an actual debugger for Python and you don't mind using a different text editor, you could try VSCode: https://code.visualstudio.com/ and download the python debugger plugin, which lets you watch variables and set breakpoints much like Visual Studio or XCode, or you could try the community version of PyCharm: https://www.jetbrains.com/pycharm/ which has a debugger built in.
Try atom-ide-debugger-python. It runs with atom's ide-python and allows variable watching as well as breakpoint setting.
Edit 2020-09: since facebook abandoned the atom-ide project, atom-ide-debugger-python has been unmaintained.