how to set the orientation of the stimulus for each trial in psychopy

I am fairly new to the python language and psychopy. I am practicing it by creating dummy experiments. Here, I am trying to create an experiment about bayesian brain. Non-vertical lines will be presented to the participant while no respond is expected from the participants, just exposure. Then for the last trial (it stays on the monitor for longer period of time to be responded), it is expected from the participant to judge whether the last line trial is vertical or not? (after exposing to non-vertical lines, I am expecting to see a change in perception of verticality).

However, there are so many things that I couldn't learn from the web. I am pretty sure you guys can help me easily.

My primary problem is; how to set up the orientation of the line? I found out the stim.ori but not sure how to use it on 'line' stimuli. Below I've attached the codes that I made so far. Also, I have added some extra questions with #.

I tried to be clear as much as I can. Sorry for my bad english. Thank you!

from psychopy import visual, core, event #import some libraries from PsychoPy
import random

#create a window
mywin = visual.Window([800,600],monitor="testMonitor", units="deg")

#stimuli
lineo = visual.Line(mywin, start=(-5, -1), end=(-5, 1))
fixation = visual.GratingStim(mywin, size=0.2, pos=[0,0], color = 'black')

#draw the stimuli and update the window
n = 5 # trial number
i = 0
while i < n:
    #fixation
    fixation.draw()
    mywin.flip()
    presses = event.waitKeys(1)
    # stimulus
    orientationlist = [20,30,40,50,60] # I want to draw the orientation info from this list
    x = random.choice(orientationlist)
    lineo.ori((x)) #
    lineo.draw()
    mywin.flip()
    presses= event.waitKeys(2)
    i +=1
    if i == 5: # how do I change the number into the length of the trial; len(int(n) didnt work.
        lineo.draw()
        mywin.flip()
        presses = event.waitKeys(4)
    #quiting
    # I dont know how to command psychopy for quiting the
    # experiment when 'escape' is pressed.

#cleanup
mywin.close()
core.quit()

Solution

There's a few things that you would want to do differently. I've updated your code and marked changes with the comment "CHANGE". Changing the orientation of a stimulus is pretty consistent in psychopy, so it's no different for Line than any other visual stimulus type.

from psychopy import visual, core, event #import some libraries from PsychoPy
import random

#create a window
mywin = visual.Window([800,600],monitor="testMonitor", units="deg")

#stimuli
lineo = visual.Line(mywin, start=(-5, -1), end=(-5, 1))
fixation = visual.GratingStim(mywin, size=0.2, pos=[0,0], color = 'black')

orientationlist = [20,30,40,50,60] # CHANGED. No need to redefine on every iteration of the while-loop.
#draw the stimuli and update the window
n = 5 # trial number

for i in range(n):  # CHANGED. This is much neater in your case than a while loop. No need to "manually" increment i.
    #fixation
    fixation.draw()
    mywin.flip()
    event.waitKeys(1)  # CHANGED. No need to assign output to anything if it isn't used.
    # stimulus

    lineo.ori = random.choice(orientationlist)  # CHANGED. Alternative: lineo.setOri(random.choice(orientationlist)).
    lineo.draw()
    mywin.flip()
    event.waitKeys(2)

# At this point, all the stimuli have been shown. So no need to do an if-statement within the loop. The following code will run at the appropriate time
lineo.draw()
mywin.flip()
event.waitKeys(keyList=['escape'])  # CHANGED. Listen for escape, do not assign to variable
# CHANGED. No need to call core.quit() or myWin.close() here since python automatically cleans everything up on script end.