Certain comparison operations misbehaving for period dtype #28980
Description
This is closely related to #28930.
import pandas as pd
s = pd.Series([pd.Period("2019"), pd.Period("2020")], dtype="period[A-DEC]")
s == "a" yields
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-4-3a654234a428> in <module>
----> 1 s == "a"
~/pandas/pandas/core/ops/__init__.py in wrapper(self, other)
527 rvalues = extract_array(other, extract_numpy=True)
528
--> 529 res_values = comparison_op(lvalues, rvalues, op)
530
531 return _construct_result(self, res_values, index=self.index, name=res_name)
~/pandas/pandas/core/ops/array_ops.py in comparison_op(left, right, op)
253
254 if should_extension_dispatch(lvalues, rvalues):
--> 255 res_values = dispatch_to_extension_op(op, lvalues, rvalues)
256
257 elif is_scalar(rvalues) and isna(rvalues):
~/pandas/pandas/core/ops/dispatch.py in dispatch_to_extension_op(op, left, right, keep_null_freq)
134
135 try:
--> 136 res_values = op(left, right)
137 except NullFrequencyError:
138 # DatetimeIndex and TimedeltaIndex with freq == None raise ValueError
~/pandas/pandas/core/arrays/period.py in wrapper(self, other)
98 result.fill(nat_result)
99 else:
--> 100 other = Period(other, freq=self.freq)
101 result = ordinal_op(other.ordinal)
102
~/pandas/pandas/_libs/tslibs/period.pyx in pandas._libs.tslibs.period.Period.__new__()
2459 value = str(value)
2460 value = value.upper()
-> 2461 dt, _, reso = parse_time_string(value, freq)
2462 if dt is NaT:
2463 ordinal = NPY_NAT
~/pandas/pandas/_libs/tslibs/parsing.pyx in pandas._libs.tslibs.parsing.parse_time_string()
265 yearfirst = get_option("display.date_yearfirst")
266
--> 267 res = parse_datetime_string_with_reso(arg, freq=freq,
268 dayfirst=dayfirst,
269 yearfirst=yearfirst)
~/pandas/pandas/_libs/tslibs/parsing.pyx in pandas._libs.tslibs.parsing.parse_datetime_string_with_reso()
291
292 if not _does_string_look_like_datetime(date_string):
--> 293 raise ValueError('Given date string not likely a datetime.')
294
295 parsed, reso = _parse_delimited_date(date_string, dayfirst)
ValueError: Given date string not likely a datetime.
but the output should be Series([False, False]). The other comparison operators <, <=, >, and >= yield the same error, which also seems incorrect (the error message should probably be different, and the error should be a TypeError rather than a ValueError). This is happening on 0.25.1 and master.