Try this:
nest = [[0,0,0,0,0],[0,0,0,0,0],[0,0,0,0,0]]
x = 1
y = 3
for array in nest:
for i in range(x, y+1):
array[i] = 1
print(nest)
I think you would benefit from a basic Python tutorial too, for example try codecademy.com.
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solved Python – Replacing Indice Values in Nested Lists