Delete line before and after needle

[nilamo]

Or, just don't write a line unless the previous line is fine.

text_to_avoid = "bad"

with open("original.txt") as infile:
    with open("out.txt", "w") as outfile:
        last_line = ""
        line_before_last = ""
        for ndx, line in enumerate(infile):
            if ndx >= 2:
                if text_to_avoid not in line.lower() \
                        and text_to_avoid not in last_line.lower() \
                        and text_to_avoid not in line_before_last.lower():
                    print(last_line, file=outfile)
            line_before_last = last_line
            last_line = line
        if text_to_avoid not in last_line.lower() \
                and text_to_avoid not in line_before_last.lower():
            print(last_line, file=outfile)