Understanding YUV to BGR color spaces conversion

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I read a BGR image:

bgr=cv2.imread('bgr.png')

I convert it to YUV color space:

yuv=cv2.cvtColor(bgr,cv2.COLOR_BGR2YUV)

Now I set U and V values of yuv image to 0:

for i in range(yuv.shape[0]):
    for j in range(yuv.shape[1]):
         yuv[i,j,1]=0
         yuv[i,j,2]=0

Now I convert yuv to BGR and display it:

BGR=cv2.cvtColor(yuv,cv2.COLOR_YUV2BGR)
cv2.imshow('BGR',BGR)

The problem is that BGR is displayed totally green (Blue and Red channels are always 0 on all the pixels)

Does this mean that Y in YUV color space is saved as G in BGR when we convert an image from YUV to BGR colorspaces ?