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Why does append() overwrite/clobber every existing element of a list with the one that was just appended?

M = []

L = [0 for i in range(10)]

print L

M.append(L)

print M

L[0] +=1

L[7] +=1

print L

M.append(L)

print M

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

[[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]]

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

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

Why does append() overwrite/clobber every existing element of a list with the one that was just appended?

M = [][] L = [0 for i in range(10)]range(10)] print L M.append(L) print LM L[0] +=1 M.append(L)L[7] +=1 print L M.append(L) print MM L[0] +=1 L[7] +=1 print L M.append(L) print M [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]0] [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]]0]] [1, 0, 0, 0, 0, 0, 0, 1, 0, 0]0] [[1, 0, 0, 0, 0, 0, 0, 1, 0, 0], [1, 0, 0, 0, 0, 0, 0, 1, 0, 0]] 0]]