REF/PERF: PeriodEngine covers narrow type

[proost]

Code Sample, a copy-pastable example if possible

pi = pd.period_range(start=2000, end=2019, freq="A")

p = pd.Period(2010, freq="A")

In [7]: pi._engine.get_loc(p)                                                   
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-7-cd77985ba7c9> in <module>
----> 1 pi._engine.get_loc(p)

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index_class_helper.pxi in pandas._libs.index.Int64Engine._check_type()

KeyError: Period('2010', 'A-DEC')

Problem description

When i handled #28628, i found PeriodEngine only works for Int type. So PeriodIndex.get_loc compute twice because PeriodEngine.get_loc only accepts Int type.

Suggestion

.get_loc on PeriodIndex computes once. Either expanding PeriodEngine.get_loc accept data type or removeing PeriodEngine.get_loc are ok

Output of pd.show_versions()

[paste the output of pd.show_versions() here below this line]
INSTALLED VERSIONS

commit : None
python : 3.7.1.final.0
python-bits : 64
OS : Linux
OS-release : 5.0.0-31-generic
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : ko_KR.UTF-8
LOCALE : ko_KR.UTF-8

pandas : 0.25.1
numpy : 1.16.1
pytz : 2018.7
dateutil : 2.7.5
pip : 19.3
setuptools : 40.6.3
Cython : 0.29.2
pytest : 5.1.0
hypothesis : None
sphinx : 1.8.2
blosc : None
feather : None
xlsxwriter : 1.1.2
lxml.etree : 4.2.5
html5lib : 1.0.1
pymysql : 0.9.3
psycopg2 : None
jinja2 : 2.10.1
IPython : 7.2.0
pandas_datareader: None
bs4 : 4.8.0
bottleneck : 1.2.1
fastparquet : None
gcsfs : None
lxml.etree : 4.2.5
matplotlib : 3.0.2
numexpr : 2.6.8
odfpy : None
openpyxl : 2.5.12
pandas_gbq : None
pyarrow : None
pytables : None
s3fs : None
scipy : 1.1.0
sqlalchemy : 1.2.15
tables : 3.4.4
xarray : None
xlrd : 1.2.0
xlwt : 1.3.0
xlsxwriter : 1.1.2

[jbrockmendel]

Does pi.get_loc work as expected? I haven't checked, but it wouldn't surprise me if PeriodEngine isn't supposed to accept a Period object

[proost]

@jbrockmendel
Yes.

pi._engine.get_loc("2010") 
pi._engine.get_loc(2010)
pi = pd.period_range(start=2000,end=2019,freq="d")
d = datetime.datetime(2010,1,1)
pi._engine.get_loc(d)

all raises exception.
PeriodEngine.get_loc always called when PeriodIndex.get_loccalled. So Why we call function which can do nothing?

And DatetimeEngine.get_loc can find location with Timestamp or datetime object.
So if use PeriodEngine.get_loc , should PeriodEngine handle Period?

What i expect is
if use PeriodEngine.get_locwhen using PeriodIndex.get_loc, fix PeriodEngine.get_loc
or abandon calling PeriodEngine.get_loc when using PeriodIndex.get_loc

[proost]

Close Issue.
I try to change the code in two way.
First, I try to remove PeriodEngine.get_loc in PeriodIndex.get_loc, so just compute .get_loc once, not several in try .. except statement. But problem is test case change inevitable. I give it up this way.
Second, I try to change PeriodEngine.get_loc to accept "Period" object not only "Period.ordinal". (Original PeriodEngine.get_loc only accept "Period.ordinal") This way is success in that work successfully and pass test cases. However Problem is most cases user don't use "Period" object using PeriodIndex.get_loc And PeriodEngine.get_loc can't accept "intolerance" argument.
Finally, Integrating PeriodIndex.get_loc fails. Close issue