All of a sudden Pycharm doesn't run anymore (select valid interpreter)

[Luke_Drillbrain]

I've done a whole bunch of coding in Pycharm.  Now all of a sudden it won't run any of my Python files anymore.  It pulled up this menu:



As you can see, it's demanding that I select a valid Python interpreter.  However, when I try to choose one from the drop-down list, the only thing available is "Project Default (none)." 

What gives?  This thing was working before.  My coding files still run in Geany. 

OS = Kubuntu Linux 16.04 LTS.  I haven't made any significant changes to the OS.  I did install the trial version of a help authoring tool named HelpBlocks.  I also needed to reinstall the Kubuntu software install library, Discover.  That shouldn't have affected Python's availability in PyCharm.

Edit: Now that I think about it, I did allow Pycharm to update itself.

Second edit: I seem to have found the interpreter in the configuration and now it works.  I guess the update must have deselected it.

[buran]

That is per-script configuration menu. Select default interpreter under Settings->Project Interpreter