python - I don't really understand how to get the output for this code - 


lst = [[2, 3, 4], [1, 1]] sum = 0 in range(len(lst)):     j in range(len(lst)):         sum += lst[i][j] print(sum)

i'm new python, can explain how output 7?

both of loops go on range of len(lst), while inner 1 should loop on range of len(lst[i]). real fix this, however, not loop on range(len(...)) loop on elements:

for sub_list in lst:   # loop on each list inside of lst     value in sub_list:  # loop on each number in sub list         sum += value

this cleaner, less prone bugs yours, , reads better.


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