Traffic light program using while loop in python - traffic

Question

I am trying to run this code in python and I want the code to stop looping when the user enters 30, here I have used break to stop the loop, is there any other way? Any suggestion would be helpful.
`x = input("Enter value: ")
stop_light = int(x)
while True:
if stop_light >= 1 and stop_light < 10:
print('Green light')
stop_light += 1
elif stop_light < 20:
print('Yellow light')
stop_light += 1
elif stop_light < 30:
print("Red light")
stop_light += 1
else:
stop_light = 0
break`

Answer 1

Hm I'm not quite sure what you actually want to achieve. Your version does not loop since the break statement will always be met after the first iteration.
Additionally, you only ask for user input once before the loop actually starts.
Here is what I suppose you want to do, so I moved the user input part inside the loop and added the break condition to the pythonic "switch" statement. This will just ask the user for input for as long as he doesn't enter 30.
while True:
x = input("Enter value: ")
stop_light = int(x)
if stop_light == 30:
break
elif stop_light >= 1 and stop_light < 10:
print('Green light')
stop_light += 1
elif stop_light < 20:
print('Yellow light')
stop_light += 1
elif stop_light < 30:
print("Red light")
stop_light += 1
else:
stop_light = 0

Answer 2

As I have already mentioned, your code does not loop. However, this code does:
while True:
try:
x = input("Enter value: ")
stop_light = int(x)
except ValueError:
print("Try Again")
else:
break
while stop_light <= 30:
if stop_light >= 1 and stop_light < 10:
print('Green light')
elif stop_light < 20:
print('Yellow light')
elif stop_light < 30:
print("Red light")
stop_light += 1
In this, I am utilizing a condition in the while loop. The condition is for the loop to iterate the user value until it becomes 30. The reason for this is because of your condition in the Red light line. I explained this further in the Problem #2 below.
Take notice that I am catching ValueError before proceeding.
Also there is only one of stop_light += 1.
Here are some sample outputs:
Enter value: asdf
Try Again
Enter value: 27
Red light
Red light
Red light
# Breaks and closes the code.
Enter value: 5
Green light
Green light
Green light
Green light
Green light
Yellow light
Yellow light
Yellow light
Yellow light
Yellow light
Yellow light
Yellow light
Yellow light
Yellow light
Yellow light
Red light
Red light
Red light
Red light
Red light
Red light
Red light
Red light
Red light
Red light
# Breaks and closes the code.
Now, these are the problems with your code:
Problem #1
else:
stop_light = 0
This portion doesn't properly handle negative numbers and numbers greater than 30. I don't think you wanted to iterate 30 times for the values that fall into that condition since you didn't apply stop_light += 1 in your code. So, you definitely have to think about what the purpose of this is.
Check out the following code that constantly loops until the value is greater than 30:
while True:
try:
x = input("Enter value: ")
stop_light = int(x)
except ValueError:
print("Try Again")
else:
while stop_light < 30:
if stop_light >= 1 and stop_light < 10:
print('Green light')
elif stop_light < 20:
print('Yellow light')
elif stop_light < 30:
print("Red light")
stop_light += 1
if stop_light > 30:
break
Output:
Enter value: asdf
Try Again
Enter value: 27
Red light
Red light
Red light
Enter value: 31
# Breaks and closes the code.
Problem #2
The reason why I scripted to loop until the value is greater than 30 is because of the following lines in your code:
elif stop_light < 30:
print("Red light")
stop_light += 1
If you wanted the loop to break only when the user inputs 30, then those lines of code above works against that theory. Your loop will break even when stop_light is 29 due to the incrementation of stop_light. You should also look into this flaw of your logic.