PERF: Timestamp/Timedelta constructors when passed a Timestamp/Timedelta #30543
Description
The Timestamp constructor's performance could be improved when an existing Timestamp object is passed to it via an isinstance-like check:
In [1]: import pandas as pd; pd.__version__
Out[1]: '0.26.0.dev0+1469.ge817ffff3'
In [2]: ts = pd.Timestamp('2020')
In [3]: def timestamp_isinstance_shortcircuit(ts):
...: if isinstance(ts, pd.Timestamp):
...: return ts
...: return pd.Timestamp(ts)
...:
In [4]: %timeit pd.Timestamp(ts)
849 ns ± 13.2 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [5]: %timeit timestamp_isinstance_shortcircuit(ts)
121 ns ± 0.279 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)Some care is needed in the constructor to check if other arguments have been passed, e.g. tz, where we wouldn't be able to directly return the Timestamp object.
Similar story for the Timedelta constructor (should be done in a separate PR):
In [6]: td = pd.Timedelta('1 day')
In [7]: def timedelta_isinstance_shortcircuit(td):
...: if isinstance(td, pd.Timedelta):
...: return td
...: return pd.Timedelta(td)
...:
In [8]: %timeit pd.Timedelta(td)
800 ns ± 1.35 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [9]: %timeit timedelta_isinstance_shortcircuit(td)
120 ns ± 0.269 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)xref #30520