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Conway Python implementation issue

I am currently working on Conway Game of Life and am stuck. My code doesn't work.

When I run my code in the GUI it says:

 
[[0 0 0 0]
 [0 1 1 0]
 [0 1 0 0]
 [0 0 0 0]]

Traceback (most recent call last):
  File "C: \ Users \ Documents \ Physics \ Python \ MainProject \ conway.py", line 53, in 
    b = apply_rules (a)
  File "C: \ Users \ Documents \ Physics \ Python \ MainProject \ conway.py", line 14, in apply_rules
    neighbors = number_neighbors (universe_array, iy, ix)
  File "C: \ Users \ Documents \ Physics \ Python \ MainProject \ conway.py", line 36, in number_neighbors
    neighbors + = 1
UnboundLocalError: local variable 'neighbors' referenced before assignment

Here is my code:

'''If a cell is dead at time T with exactly three live neighbours, the cell will be alive at T+1
If a cell is alive at time T with less than two living neighbours it dies at T+1
If a cell is alive at time T with more than three live neighbours it dies at T+1
If a cell is alive at time T with exactly two or three live neighbours it remains alive at T+1'''
import numpy


def apply_rules (universe_array):
    height, width = universe_array.shape
    # create a new array for t+1
    evolved_array = numpy.zeros((height, width),numpy.uint8)
    for iy in range(1, height-1):
        for ix in range(1,width-1):
            neighbours=number_neighbours(universe_array,iy,ix)
            if universe_array[iy,ix]==0 and neighbours==3:
                evolved_array[iy,ix]==1
            elif universe_array[iy,ix]==1 and neighbours<2:
                evolved_array[iy,ix]==0
            elif universe_array[iy,ix]==1 and neighbours>3:
                evolved_array[iy,ix]==0
            elif universe_array[iy,ix]==1 and neighbours==2 or neighbours==3:
                evolved_array[iy,ix]=universe_array[iy,ix]

    return evolved_array

def number_neighbours(universe_array,iy,ix):
    neighbours=0 #fixed this line,thanks:)
    if universe_array[iy-1,ix-1]==1:
            neighbours+=1
    if universe_array[iy,ix-1]==1:
            neighbours+=1
    if universe_array[iy+1,ix-1]==1:
            neighbours+=1
    if universe_array[iy-1,ix]==1:
            neighbours+=1
    if universe_array[iy+1,ix]==1:
            neighbours+=1
    if universe_array[iy-1,ix+1]==1:
            neighbours+=1
    if universe_array[iy,ix+1]==1:
            neighbours+=1
    if universe_array[iy+1,ix+1]==1:
            neighbours+=1
    else:
        neighbours=neighbours
    return neighbours

if __name__ == "__main__":
    a = numpy.zeros((4,4),numpy.uint8)
    a[1,1]=1
    a[1,2]=1
    a[2,1]=1
    print a
    b= apply_rules(a)
    print b

I am a beginner in Python and I have no idea how to fix the error. I'm a little confused about import "neighbours"

before function "apply_rules"

, is this the correct way to do it?

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4 answers


Well, I think you are also completely new to programming as such, otherwise you should have no problem interpreting this simple error message.

I'll help you dispel it:

  • First, all the "current" line numbers of your project files are displayed in the order they are called.
  • Then it shows you the function where the error occurred: number_neighbours

  • Then the contents of the line containing the error will be displayed: neighbours+=1

  • Finally, it informs you that the problem is with this line: UnboundLocalError: local variable 'neighbours' referenced before assignment



Now what does this mean? Let's see what the operator does +=

: it adds something to the current value neighbours

. This means that it reads the current value, adds something to it, and finally saves it back. "Reading" is called "reference" relative to variables.

What is the current value neighbours

? Well, it has never been used before, so it has no value - no value has ever been assigned to it. Adding something to "no value" is not a smart thing to do. I am assuming that you expect it to be 0, but you must inform your interpreter about this. To do this, add the following statement before the start of your function:neighbours = 0

+13


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You are trying to increment a variable that doesn't exist yet. Python cannot increment something if it doesn't know what it is. Try adding the following line at the top of the def number_neighbors function.



neighbours = 0
+3


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A quick glance reveals that your indexes are number_neighbors

off.

Also, you never initialize neighbors

.

Reply to comment:

def number_neighbours(universe_array,iy,ix):
    if universe_array[iy,ix-1]==1:
        neighbours+=1
    if universe_array[iy,ix-1]==1:
        neighbours+=1
    if universe_array[iy+1,ix-1]==1:
        neighbours+=1

You say neighbors +=1

what adding 1 to means neighbors

, but you never told him to start at 0, so he doesn't know what to add 1 to.

Also note that the first and third lines are exactly the same. I'm pretty sure this is not what you intended. This is what I mean by "your metrics are disabled".

Answer to comment 2: apply_rules

Has multiple lines where you want to assign a value to something (which is '='), but you use '==' instead.

+2


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This is an extremely low class lazy question, but the number_neighbors function is broken, it double-checks the universe [iy, ix-1] (and therefore omits the check it should do).

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