Well if you are trying to get a single input when a key is presses I suggest using 'On key pressed.' The difference is, with 'iskeypressed' it is checking if the key is being pressed at the moment, almost like a while loop. But 'on the key pressed' it simply checks when the key is first pressed and returns True.
Example: On 'up arrow' pressed = Jump
is 'up arrow' pressed = keep jumping while true
Sorry if this is really wordy. I hope this helps you, and you make progress!