python - Editing a duplicate list edits the original -

so i've started simple sort of roguelike game project in python, have problems editing duplicate list editing original. code follows:

charx = 1 chary = 1 level = [["#","#","#","#","#","#","#"],["#",".",".",".",".",".","#"],["#",".","#",".",".",".","#"],["#","#","#","#","#","#","#"]] while true:     move = raw_input("u,d,l or r: ")     if move=="u":         if level[chary-1][charx]!="#":             chary-=1     elif move=="d":         if level[chary+1][charx]!="#":             chary+=1     elif move=="r":         if level[chary][charx+1]!="#":             charx+=1     elif move=="l":         if level[chary][charx-1]!="#":             charx-=1     display_level=level     display_level[chary][charx]="@"     row in display_level:         print "".join(row)     row2 in level:         print ",".join(row2) 

as can see have created list called level, each list inside list row. characters starting row , column position stated.

then loop asks whether want move up, down left or right. checks see if there wall (the # character) in way , reacts accordingly.

as can see, makes duplicate of level called display_level , puts "@" character onto display level. problem changing display_level changes level no apparent reason, though separate , each time loop runs through makes display_level=level.

display_level , level printed separately , shows level being edited along side display_level shouldn't happen.

so want know why changing part of display_level change level , how can fix it.

much appreciated

you not creating duplicate of level. create reference same list.

to create copy of list, can slice start end:

display_level = level[:] 

but case, not enough. need copy nested lists. in case, list comprehension easiest:

display_level = [l[:] l in level] 

a more comprehensive solution use copy.deepcopy() function make absolutely sure top-level object , contained objects copies:

import copy  # ...  display_level = copy.deepcopy(level)