python - Initialise list correctly -

i reading file line line. each line read in such gets split list (of length 13) contains sublists (of arbitrary length (usually between 1 , four). mandated data structure of file reading.

i carry out check on each line see if contains desired data , want save if does.

it saved list (called results) containing 13 fields, each again containing several lists obtain structure following: results[0] = [line1[0], line2[0], ...]; results[1] = [line1[1], line2[1], ...]; ...; results[12] = [line1[12], line2[12], ...] (results[i][j] list of length 1 containing string).

i solve by:

results = [] in line:     results[i].append(line[i]) 

to though list results needs initialised first can't manually don't know if first line contains entry want save priori , don't want initialise random values have delete later deleting first entry in list quite inefficient far know. how solve problem?

if know need hold 13 sub-lists, create 13 empty lists:

results = [[] _ in range(13)] 

note: cannot do:

results = [[]] * 13 

because mirror reference single list 13 times; mutating entry mutate of them. see this answer more details.