Issue 1:
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

Issue 2:
use max_seq_len, after setting default to close #3391.

also duplicate behaviour of "..." in other situations, rather then

always printing 6 items