text: import numpy as np
  import pytest
  
  import pandas as pd
  from pandas import PeriodIndex, period_range
  import pandas._testing as tm
  
  
  class TestPeriodIndexShift:
      # ---------------------------------------------------------------
      # PeriodIndex.shift is used by __add__ and __sub__
  
      def test_pi_shift_ndarray(self):
          idx = PeriodIndex(
              ["2011-01", "2011-02", "NaT", "2011-04"], freq="M", name="idx"
          )
          result = idx.shift(np.array([1, 2, 3, 4]))
          expected = PeriodIndex(
              ["2011-02", "2011-04", "NaT", "2011-08"], freq="M", name="idx"
          )
          tm.assert_index_equal(result, expected)
  
          result = idx.shift(np.array([1, -2, 3, -4]))
          expected = PeriodIndex(
              ["2011-02", "2010-12", "NaT", "2010-12"], freq="M", name="idx"
          )
          tm.assert_index_equal(result, expected)
  
      def test_shift(self):
          pi1 = period_range(freq="A", start="1/1/2001", end="12/1/2009")
          pi2 = period_range(freq="A", start="1/1/2002", end="12/1/2010")
  
          tm.assert_index_equal(pi1.shift(0), pi1)
  
          assert len(pi1) == len(pi2)
          tm.assert_index_equal(pi1.shift(1), pi2)
  
          pi1 = period_range(freq="A", start="1/1/2001", end="12/1/2009")
          pi2 = period_range(freq="A", start="1/1/2000", end="12/1/2008")
          assert len(pi1) == len(pi2)
          tm.assert_index_equal(pi1.shift(-1), pi2)
  
          pi1 = period_range(freq="M", start="1/1/2001", end="12/1/2009")
          pi2 = period_range(freq="M", start="2/1/2001", end="1/1/2010")
          assert len(pi1) == len(pi2)
          tm.assert_index_equal(pi1.shift(1), pi2)
  
          pi1 = period_range(freq="M", start="1/1/2001", end="12/1/2009")
          pi2 = period_range(freq="M", start="12/1/2000", end="11/1/2009")
          assert len(pi1) == len(pi2)
          tm.assert_index_equal(pi1.shift(-1), pi2)
  
          pi1 = period_range(freq="D", start="1/1/2001", end="12/1/2009")
          pi2 = period_range(freq="D", start="1/2/2001", end="12/2/2009")
          assert len(pi1) == len(pi2)
          tm.assert_index_equal(pi1.shift(1), pi2)
  
          pi1 = period_range(freq="D", start="1/1/2001", end="12/1/2009")
          pi2 = period_range(freq="D", start="12/31/2000", end="11/30/2009")
          assert len(pi1) == len(pi2)
          tm.assert_index_equal(pi1.shift(-1), pi2)
  
      def test_shift_corner_cases(self):
          # GH#9903
          idx = pd.PeriodIndex([], name="xxx", freq="H")
  
          with pytest.raises(TypeError):
              # period shift doesn't accept freq
              idx.shift(1, freq="H")
  
          tm.assert_index_equal(idx.shift(0), idx)
          tm.assert_index_equal(idx.shift(3), idx)
  
          idx = pd.PeriodIndex(
              ["2011-01-01 10:00", "2011-01-01 11:00", "2011-01-01 12:00"],
              name="xxx",
              freq="H",
          )
          tm.assert_index_equal(idx.shift(0), idx)
          exp = pd.PeriodIndex(
              ["2011-01-01 13:00", "2011-01-01 14:00", "2011-01-01 15:00"],
              name="xxx",
              freq="H",
          )
          tm.assert_index_equal(idx.shift(3), exp)
          exp = pd.PeriodIndex(
              ["2011-01-01 07:00", "2011-01-01 08:00", "2011-01-01 09:00"],
              name="xxx",
              freq="H",
          )
          tm.assert_index_equal(idx.shift(-3), exp)
  
      def test_shift_nat(self):
          idx = PeriodIndex(
              ["2011-01", "2011-02", "NaT", "2011-04"], freq="M", name="idx"
          )
          result = idx.shift(1)
          expected = PeriodIndex(
              ["2011-02", "2011-03", "NaT", "2011-05"], freq="M", name="idx"
          )
          tm.assert_index_equal(result, expected)
          assert result.name == expected.name
  
      def test_shift_gh8083(self):
          # test shift for PeriodIndex
          # GH#8083
          drange = pd.period_range("20130101", periods=5, freq="D")
          result = drange.shift(1)
          expected = PeriodIndex(
              ["2013-01-02", "2013-01-03", "2013-01-04", "2013-01-05", "2013-01-06"],
              freq="D",
          )
          tm.assert_index_equal(result, expected)
  
      def test_shift_periods(self):
          # GH #22458 : argument 'n' was deprecated in favor of 'periods'
          idx = period_range(freq="A", start="1/1/2001", end="12/1/2009")
          tm.assert_index_equal(idx.shift(periods=0), idx)
          tm.assert_index_equal(idx.shift(0), idx)
  