Randomly walking turtle function not doing what I want it to

Question

I have to write a programme where a turtle takes 90 degree turns, chosen randomly as left or right, around the screen, until it hits a wall, takes a 180 degree turn and goes back to walking around the screen. When it's hit the wall 4 times, the loop terminates. The problem I'm having is that when it bounces off the wall it just stops walking, and the loop has clearly terminated as I can close the window by clicking on it (wn.exitonclick). Here's the full programme:

import turtle
import random

def isInScreen(w,t):
    leftBound = w.window_width() / -2
    rightBound = w.window_width() / 2
    bottomBound = w.window_height() / -2
    topBound = w.window_height() / 2

    turtlex = t.xcor()
    turtley = t.ycor()

    stillIn = True

    if turtlex < leftBound or turtlex > rightBound or turtley < bottomBound or turtley > topBound:
        stillIn = False

    return(stillIn)

def randomWalk(t,w):
    counter = 0

    while isInScreen(w,t) and counter < 4:
        coin = random.randrange(0,2)
        if coin == 0:
            t.left(90)
        else:
            t.right(90)
        t.forward(50)

    t.left(180)
    t.forward(50)
    counter = counter+1

wn = turtle.Screen()
wn.bgcolor('lightcyan')

steklovata = turtle.Turtle()
steklovata.color('darkslategray')
steklovata.shape('turtle')

randomWalk(steklovata,wn)

wn.exitonclick()

I'm confused as to why it stops, considering once the turtle bounces back, its x and y coordinates meet the requirements for isInScreen(w,t) to be true and thus go back to walking. Any ideas?

EDIT: Accepted Sukrit's answer as it was the easiest to relate to what I'd already programmed and gave me a few pointers on other stuff, but Brian's answer was very useful too and I'd accept both if it was possible. Thanks a lot to both of you!

Answer 1

Your counter = counter + 1 is wrong. When your isInScreen returns False, the while loop breaks and the code ends, since, the counter is being incremented but you don't loop over again. See the following code -

import turtle
import random

def isInScreen(w,t):
    leftBound = w.window_width() / -2.0
    rightBound = w.window_width() / 2.0
    bottomBound = w.window_height() / -2.0
    topBound = w.window_height() / 2.0

    turtlex = t.xcor()
    turtley = t.ycor()

    if turtlex < leftBound or turtlex > rightBound or turtley < bottomBound or turtley > topBound:
        return False

    return True

def randomWalk(t,w):
    counter = 0

    while True:
        while isInScreen(w,t):
            coin = random.randrange(0,2)
            if coin == 0:
                t.left(90)
            else:
                t.right(90)
            t.forward(50)
        t.left(180)
        t.forward(50)
        counter += 1
        if counter == 4:
            break

wn = turtle.Screen()
wn.bgcolor('lightcyan')

steklovata = turtle.Turtle()
steklovata.color('darkslategray')
steklovata.shape('turtle')

randomWalk(steklovata,wn)

wn.exitonclick()

P.S - You don't need a variable to store stillIn, if the if condition evaluates to True, just return False, and if it doesn't return True. (Changes reflected in the above code).