def get_lines_from_file(filename, lineno, context_lines, loader=None, module_name=None):
    """
    Returns context_lines before and after lineno from file.
    Returns (pre_context_lineno, pre_context, context_line, post_context).
    """
    lineno = lineno - 1
    lower_bound = max(0, lineno - context_lines)
    upper_bound = lineno + context_lines

    source = None
    if loader is not None and hasattr(loader, "get_source"):
        result = get_source_lines_from_loader(loader, module_name, lineno, lower_bound, upper_bound)
        if result is not None:
            return result

    if source is None:
        try:
            with open(filename, "rb") as file_obj:
                encoding = "utf8"
                # try to find encoding of source file by "coding" header
                # if none is found, utf8 is used as a fallback
                for line in itertools.islice(file_obj, 0, 2):
                    match = _coding_re.search(line.decode("utf8"))
                    if match:
                        encoding = match.group(1)
                        break
                file_obj.seek(0)
                lines = [
                    compat.text_type(line, encoding, "replace")
                    for line in itertools.islice(file_obj, lower_bound, upper_bound + 1)
                ]
                offset = lineno - lower_bound
                return (
                    [l.strip("\r\n") for l in lines[0:offset]],
                    lines[offset].strip("\r\n"),
                    [l.strip("\r\n") for l in lines[offset + 1 :]] if len(lines) > offset else [],
                )
        except (OSError, IOError, IndexError):
            pass
    return None, None, None
Returns context_lines before and after lineno from file.
    Returns (pre_context_lineno, pre_context, context_line, post_context).