numpy - Python matrix loops -

i have python code expected output matrix same size of input matrix. output value @ [i,j] should equal twice sum of d[i-1,j] , d[i,j] , add ouput @ instance [i-1,j] it. code follows

import numpy np  d=((2,3,5,6),(4,6,7,9),(8,4,7,3),(1,7,3,9),(5,8,2,6)) d=np.matrix(d) r,c = np.shape(d)  temp=[] y=[] y.append([0,0,0,0])  in range (r-1):     ro = d[i:i+2,:]     #fetch 2 rows @ time i.e. , i+1     j in range (c):                 col = ro[:,j]   #fetch 1 column of row         v1 = int(col[0])         v2 = int(col[1])          x = (v1+v2)*2+int(y[i][j])         temp.append(x)     y.append(temp) y = np.matrix(y) print y 

expected output is

[[0,0,0,0]  [12,18,24,30]  [36,38,52,54]  [54,60,72,78]  [66,90,82,108]] 

but instead get:

[[[0, 0, 0, 0]   [12, 18, 24, 30, 36, 38, 52, 54, 30, 40, 44, 54, 24, 48, 34, 60]   [12, 18, 24, 30, 36, 38, 52, 54, 30, 40, 44, 54, 24, 48, 34, 60]   [12, 18, 24, 30, 36, 38, 52, 54, 30, 40, 44, 54, 24, 48, 34, 60]   [12, 18, 24, 30, 36, 38, 52, 54, 30, 40, 44, 54, 24, 48, 34, 60]]] 

where error in code?

you have reset temp accumulator each iteration of outer loop. code look:

...  in range (r-1):     ro = d[i:i+2,:]     #fetch 2 rows @ time i.e. , i+1     temp = []  # <-------------     j in range (c):          ... 

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the unexpected output got original code because of way python lists work: when append object python list, reference object stored, not copy of object. after loop has finished, list y looks like:

[reference [0,0,0,0],  reference list created @ line 7,  reference list created @ line 7,  reference list created @ line 7,  reference list created @ line 7] 

so last 4 references same single object!