38175 added correct handling of nanoseconds in the Period constructor but the code path as is parses the input twice. We should integrate the nanoseconds code into `parse_time_string` so this happens only once.

xref https://github.com/pandas-dev/pandas/pull/38175/files#r536100941

It might be worth adding a nanosecond Period constructor benchmark too.

Comment From: jorisvandenbossche

BTW, the reason I noted this is actually already thanks to our benchmarks: https://pandas.pydata.org/speed/pandas/#period.PeriodIndexConstructor.time_from_ints?python=3.8&Cython=0.29.21&p-freq='D'&p-is_offset=False&commits=02caf7d7-daa59420

Pandas PERF: Period constructor parses input twice

38175 added correct handling of nanoseconds in the Period constructor but the code path as is parses the input twice. We should integrate the nanoseconds code into parse_time_string so this happens only once.

38175 added correct handling of nanoseconds in the Period constructor but the code path as is parses the input twice. We should integrate the nanoseconds code into `parse_time_string` so this happens only once.