python - Abnormal list behaviour -

python - Abnormal list behaviour -

i working on problem , came across this.

python code

row=[] col=[] init=[-1,-1]

now append init row , col.

row.append(init) row.append(init) col.append(init) col.append(init)

therefore row = [[-1,-1],[-1,-1]] , col = [[-1,-1],[-1,-1]]

now when alter init[0] = 9 row , col becomes row = [[9,-1],[9,-1]] , col = [[9,-1],[9,-1]]

this happens because store same reference object init on , over. when modify object sees it.

you seek appending copies of list instead. 1 way illustration be:

row.append(list(init))

there's more 1 way clone list.

python