Pattern: line writer with indentation

line_writer.py

class LineWriter:
    def __init__(self, f, indent=0):
        self._f = f
        self._indent = indent

    def indented(self) -> "LineWriter":
        return LineWriter(self._f, self._indent + 1)

    def write_line(self, s=None):
        if s is not None:
            self._f.write("    " * self._indent + s + "\n")
        else:
            self._f.write("\n")