Python while loop with no expressions

Question

Is is possible to have a while loop in Python with no expressions? I know in other languages you can do something like:

while(flag) {};

I'm trying to do something similar in Python but cannot find an answer. Here is what I have so far:

import turtle
from random import randrange

def is_in_screen(t, w): #CHECKS TO SEE IF STILL IN SCREEN
    flag = True
    r = w.window_width() / 2
    l = r * -1
    u = w.window_height() / 2
    d = u * -1

    x_cor = t.xcor()
    y_cor = t.ycor()

    if (x_cor < l or x_cor > r or y_cor < d or y_cor > u):
        flag = False
    return flag

def move_to(t, w): #MOVE IN RANDOM DIRECTION AND RANDOM DISTANCE
    t.forward(randrange(1, 100))
    if (randrange(1, 2) == 1):
        t.left(randrange(1, 180))
    else:
        t.right(randrange(1, 180))
    return is_in_screen(t, w)

def random_movement(t1, t2, w):
    while (move_to(t1, w) and move_to(t2, w)): #<<<<<<<<LOOP IN QUESTION
        i = 0 

def main():
    t1 = turtle.Turtle()
    t2 = turtle.Turtle()
    w = turtle.Screen()

    t1.color("green")
    t2.color("purple")

    random_movement(t1, t2, w)

    w.exitonclick()

main()

The reason I'm trying to do no expressions is because I want the second turtle to not move if the first turtle goes out of bounds. Also, I do not want return statements in the function.

I think what you are looking for is the command "pass". You can put this after the while and it will do nothing in the loop. — Tyberius
– Tyberius, Commented Oct 7, 2018 at 4:23
you can go for "pass" in python.... if you want to use while without any condition means it will become always true can do it like "while True:" — abhi krishnan
– abhi krishnan, Commented Oct 7, 2018 at 4:25
Such a loop is going to block your whole program with a lot of CPU load until the condition is met. — Klaus D.
– Klaus D., Commented Oct 7, 2018 at 4:29
While you can use pass and it'll allow the program to run, code like while(<test with no side effects>): pass will hopelessly deadlock your program. Buyer beware. — jedwards
– jedwards, Commented Oct 7, 2018 at 5:12

Picachieu · Accepted Answer · 2018-10-07 04:27:13Z

8

You're looking for the pass keyword.

while (flag):
    pass

answered Oct 7, 2018 at 4:27

Picachieu

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1 Comment

Mad Physicist Over a year ago

Parens are very optional

cdlane · Accepted Answer · 2018-10-14 05:34:54Z

Below is a rework of your code with the while expr: pass that everyone's suggesting along with some other style and idiom changes to tighten up the code:

from turtle import Screen, Turtle
from random import randrange

def is_in_screen(turtle, screen):
    r = screen.window_width() / 2
    u = screen.window_height() / 2

    x, y = turtle.position()

    return -r < x < r and -u < y < u

def move_to(turtle, screen):
    turtle.forward(randrange(1, 100))

    turtle.left(randrange(-180, 180))  # negative left turn is a right turn

    return is_in_screen(turtle, screen)

def random_movement(turtle_1, turtle_2, screen):
    while move_to(turtle_1, screen) and move_to(turtle_2, screen): pass

screen = Screen()

t1 = Turtle()
t1.color("green")

t2 = Turtle()
t2.color("purple")

random_movement(t1, t2, screen)

screen.exitonclick()

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