[Python] Same program getting different output when debugged and run as script

For a sample picture, the value of start should be 7 after execution, but gives output 0 when run as script.

When debugged, it returns the correct result.

def startdetection(start):
i = 0
while( i < column):
pixel = image.getpixel((i,start))[0]
if pixel ==0:
return
elif i == column-1:
start = start +1
i = 0
else:
i = i+1
end = start + 38

startdetection(0)

print(start)

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