Python: Variables not changing

Question

My variables are not changing when I am subtracting from them. I am supposed to have the xPos and yPos change and then print out the change.

It does not have any errors.

xPos = 400 
yPos = 400 
rain = False 
sidewalk = True 

print("Your robot is located at", xPos , "on the x-axis and", yPos , "on the y-axis")

yPos - 5
xPos-100

print("Your robot is located at", xPos , "on the x-axis and", yPos , "on the y-axis")

It prints "Your robot is located at 400 on the x-axis and 400 on the y-axis" twice instead of printing that once and "Your robot is located at 300 on the x-axis and 395 on the y-axis".

You have to assign the result of the operation to something. — wwii
– wwii, Commented Sep 2, 2019 at 2:35

Djaouad · Accepted Answer · 2019-09-01 22:35:06Z

2

You are subtracting, but the results of the subtraction are not being used (because numbers are immutable, you can't change them in-place), you need to assign those results back to the variables you're subtracting from:

yPos = yPos - 5    #  or, yPos -= 5
xPos = xPos - 100  #  or, xPos -= 100

answered Sep 1, 2019 at 22:35

Djaouad

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Steve · Accepted Answer · 2019-09-01 22:36:21Z

1

You need to reallocate the subtraction to a variable. It can be the same variable if you want.

yPos = yPos - 5
xPos = xPos - 100

If you just have the lines you have the Python interpreter does the maths but has nowhere to store the result. So in the terminal you can do this:

y = 100
print(y) # prints 100
y - 5 # outputs 95
print(y) # prints 100

answered Sep 1, 2019 at 22:36

Steve

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