code: def test_period_sub_period(self):
      per1 = Period("2011-01-01", freq="D")
      per2 = Period("2011-01-15", freq="D")
  
      off = per1.freq
      assert per1 - per2 == -14 * off
      assert per2 - per1 == 14 * off
  
      msg = r"Input has different freq=M from Period\(freq=D\)"
      with pytest.raises(IncompatibleFrequency, match=msg):
          per1 - Period("2011-02", freq="M")
  
imports: from datetime import timedelta
  import numpy
  import pytest
  from pandas._libs.tslibs.period import IncompatibleFrequency
  from pandas import NaT, Period, Timedelta, Timestamp, offsets
label_desc: Use image node_id 5 for calling the TestPeriodArithmetic obj's underlying member method code with example usage: obj.test_period_sub_period() without return types