Shouldn’t that be 42 instead?

That just selects everything. And by “everything,” I mean everything: life, the universe, etc.

I thought putting it as 69 would make it clear but yes

Shouldn’t that be 42 instead? ;-)

Regardless, I was putting it into use and it’s actually worse than that. When the file has tabs, getCurrentPos() it does not line up as the position varies depending on the tabulation. How do circumvent it? I assume getColumn() might help looking at the docs. Hum…

It’s (usually) bad practice to include “magic numbers” like 69 in your code with no explanation as to why you chose that number. Better to declare a global constant (preferably with an explanatory comment) like so, and then reference it later on in the code:

# I'm using a proprietary file format where every file has 69 lines
MY_MAGIC_NUMBER = 69
...
...
for x in range(1, MY_MAGIC_NUMBER):

That may reduce your confusion weeks later when you stumble across this script and wonder what the hell it’s supposed to do.

if there is something outstandingly bad

Probably this is a leading candidate:

69

if editor.getSelectionEmpty():

  currentLine = editor.lineFromPosition(editor.getCurrentPos())
  currentLineLength = editor.lineLength(currentLine)
  currentLineStart = editor.positionFromLine(currentLine)
  
  currentPos = editor.getCurrentPos()
  currentHorizontalPos = currentPos - currentLineStart
  currentChar = editor.getTextRange(currentPos, currentPos + 1)

  for x in range(1, 69):
    previousLineStart = editor.positionFromLine(currentLine-x)
    previousLinelength = editor.lineLength(currentLine-x)
    
    if editor.lineLength(currentLine-x) < currentHorizontalPos:
      break
    
    previousLineSamePosition = previousLineStart + currentHorizontalPos
    previousChar = editor.getTextRange(previousLineSamePosition, previousLineSamePosition + 1)

    if currentChar != previousChar:
      break
    else:
      editor.addSelection(previousLineSamePosition,previousLineSamePosition)

There is better ways to do it, I assume, but it worked so far. Please tell me if there is something outstandingly bad.

so I don’t have to press Alt+Shift that many times

Well, there’s this that may help:

User manual ref..