Code Sample, a copy-pastable example if possible

>>> pr = pd.period_range(start='2017-01-01 00:00:00', periods=999999, freq='T')
>>> df = pd.DataFrame({"value": range(999999)}, index=pr)
>>> df.loc[:"2018-01-01 00:00"]
                   value
2017-01-01 00:00       0
2017-01-01 00:01       1
2017-01-01 00:02       2
...
2017-12-31 23:59  525599
2018-01-01 00:00  525600

Everything will be fine if the value of periods parameter is < 1000000.

So when I hit it with 1000000:

>>> pr = pd.period_range(start='2017-01-01 00:00:00', periods=1000000, freq='T')
>>> df = pd.DataFrame({"value": range(1000000)}, index=pr)
>>> df.loc[:"2018-01-01 00:00"]

Error occurs:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexing.py", line 1373, in __getitem__
    return self._getitem_axis(maybe_callable, axis=axis)
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexing.py", line 1581, in _getitem_axis
    return self._get_slice_axis(key, axis=axis)
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexing.py", line 1406, in _get_slice_axis
    slice_obj.step, kind=self.name)
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 3454, in slice_indexer
    kind=kind)
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 3661, in slice_locs
    end_slice = self.get_slice_bound(end, 'right', kind)
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 3585, in get_slice_bound
    slc = self._get_loc_only_exact_matches(label)
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 3554, in _get_loc_only_exact_matches
    return self.get_loc(key)
  File "/Users/violetvivirand/.local/share/virtualenvs/rewind-imputation-UYiSILLm/lib/python3.6/site-packages/pandas/core/indexes/period.py", line 812, in get_loc
    return self._engine.get_loc(key)
  File "pandas/_libs/index.pyx", line 117, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/index.pyx", line 125, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/index.pyx", line 365, in pandas._libs.index._bin_search
  File "pandas/_libs/period.pyx", line 717, in pandas._libs.period._Period.__richcmp__
TypeError: Cannot compare type 'Period' with type 'int64'

Problem description

Don't know what causes the error when the amount of PeriodIndex is more than 1000000. It should work without any problem, isn't it 😕❓

Expected Output

It should returns the data from 2017-01-01 00:00 to 2018-01-01 00:00:

                   value
2017-01-01 00:00       0
2017-01-01 00:01       1
2017-01-01 00:02       2
...
2017-12-31 23:59  525599
2018-01-01 00:00  525600

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.0.final.0 python-bits: 64 OS: Darwin OS-release: 16.7.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: zh_TW.UTF-8 LOCALE: zh_TW.UTF-8 pandas: 0.21.0 pytest: None pip: 9.0.1 setuptools: 36.6.0 Cython: None numpy: 1.13.3 scipy: None pyarrow: None xarray: None IPython: 6.2.1 sphinx: None patsy: None dateutil: 2.6.1 pytz: 2017.3 blosc: None bottleneck: None tables: None numexpr: None feather: None matplotlib: None openpyxl: None xlrd: None xlwt: None xlsxwriter: None lxml: None bs4: None html5lib: None sqlalchemy: None pymysql: None psycopg2: None jinja2: None s3fs: None fastparquet: None pandas_gbq: None pandas_datareader: None

Comment From: jreback

xref #17755, cc @Licht-T

You are doing partial string indexing on a Period. This has a number of open issues (meaning its not fully supported).

duplicated by https://github.com/pandas-dev/pandas/issues/13429 / #15920