将Matlab翻译成Python

Question

我翻译了这个matlab代码：

Down_step = 2;
aveKernel = fspecial('average',2);
aveY1 = conv2(Y1, aveKernel,'same');
aveY2 = conv2(Y2, aveKernel,'same');
Y1 = aveY1(1:Down_step:end,1:Down_step:end);
Y2 = aveY2(1:Down_step:end,1:Down_step:end);

到Python：

import numpy as np
from scipy.ndimage.filters import convolve as __convolve

Down_step = 2   
aveKernel = np.array([[1.0,1.0],[1.0,1.0]])/4 # averaging filter
aveY1 = __convolve(ref, aveKernel, mode='constant', cval=0.0) 
aveY2 = __convolve(dist, aveKernel, mode='constant', cval=0.0)

我不知道如何翻译最后两行

1:Down_step:end

部分让我感到困惑，这是什么意思？