Make pandas types inherit from datetime types (#77)

* Inheritance, still a couple of problems

* Timestamps and timedeltas now inherit from datetime classes

* Fix an issue with tox not recognizing Python 3.6 and 3.7 versions

* Go back to previous tox configuration

tests/snippets/test_timestamp.py

@@ -3,6 +3,7 @@
 import pandas as pd
 import datetime as dt
 
+
 def test_types_init() -> None:
     ts: pd.Timestamp = pd.Timestamp('2021-03-01T12')
     ts1: pd.Timestamp = pd.Timestamp(dt.date(2021, 3, 15))
@@ -14,3 +15,20 @@ def test_types_init() -> None:
     ts7: pd.Timestamp = pd.Timestamp(2021, 3, 10, 12)
     ts8: pd.Timestamp = pd.Timestamp(year=2021, month=3, day=10, hour=12)
     ts9: pd.Timestamp = pd.Timestamp(year=2021, month=3, day=10, hour=12, tz='US/Pacific')
+
+
+def test_types_arithmetic() -> None:
+    ts: pd.Timestamp = pd.to_datetime("2021-03-01")
+    ts2: pd.Timestamp = pd.to_datetime("2021-01-01")
+    delta: pd.Timedelta = pd.to_timedelta("1 day")
+
+    tsr: pd.Timedelta = ts - ts2
+    tsr2: pd.Timestamp = ts + delta
+
+
+def test_types_comparison() -> None:
+    ts: pd.Timestamp = pd.to_datetime("2021-03-01")
+    ts2: pd.Timestamp = pd.to_datetime("2021-01-01")
+
+    tsr: bool = ts < ts2
+    tsr2: bool = ts > ts2

third_party/3/pandas/_libs/tslibs/timedeltas.pyi

@@ -2,6 +2,6 @@ from datetime import timedelta
 from typing import Any, Union
 import numpy as np
 
-class Timedelta:
+class Timedelta(timedelta):
 
     def __init__(self, value: Union[Timedelta, timedelta, np.timedelta64, str, int], unit: str = ..., **kwargs: Any) -> None: ...

third_party/3/pandas/_libs/tslibs/timestamps.pyi

@@ -1,13 +1,19 @@
+"""
+This class could be comprehensibly typed with the typeshed .pyi file but the
+datatetime.datetime and pd.Timestamp API differ quite a bit and cannot be used interchangeably
+"""
 import sys
-from typing import Any, Optional, Union, overload
+from typing import Any, Optional, Union, overload, TypeVar, Type
+
+from pandas._libs.tslibs.timedeltas import Timedelta
 
 if sys.version_info >= (3, 8):
     from typing import Literal
 else:
     from typing_extensions import Literal
 
 from dateutil.tz import tzfile
-from datetime import tzinfo, date
+from datetime import tzinfo, datetime, date as _date, time, timedelta
 
 from pandas._libs.tslibs.period import Period
 from pandas._typing import TimestampConvertible
@@ -16,35 +22,52 @@ OptInt = Optional[int]
 
 Fold = Literal[0, 1]
 
-class Timestamp:
+_S = TypeVar("_S")
+
+class Timestamp(datetime):
     @overload
-    def __init__(self, ts_input: TimestampConvertible, freq: Optional[str] = ..., tz: Optional[Union[str, tzinfo, tzfile]] = ..., unit: Optional[str] = ..., tzinfo: Optional[tzinfo] = ..., fold: Optional[Fold] = ...): ...
+    def __init__(self, ts_input: TimestampConvertible, freq: Optional[str] = ..., tz: Optional[Union[str, tzinfo, tzfile]] = ...,
+                 unit: Optional[str] = ..., tzinfo: Optional[tzinfo] = ..., fold: Optional[Fold] = ...): ...
     @overload
-    def __init__(self, year: OptInt = ..., month: OptInt = ..., day: OptInt = ..., hour: OptInt = ..., minute: OptInt = ..., second: OptInt = ..., microsecond: OptInt = ..., nanosecond: OptInt = ..., tz: Optional[Union[str, tzinfo, tzfile]] = ..., tzinfo: Optional[tzinfo] = ..., fold: Optional[Fold] = ..., freq: Optional[str] = ...): ...
+    def __init__(self, year: OptInt = ..., month: OptInt = ..., day: OptInt = ..., hour: OptInt = ..., minute: OptInt = ...,
+                 second: OptInt = ..., microsecond: OptInt = ..., nanosecond: OptInt = ..., tz: Optional[Union[str, tzinfo, tzfile]] = ...,
+                 tzinfo: Optional[tzinfo] = ..., fold: Optional[Fold] = ..., freq: Optional[str] = ...): ...
     def to_period(self, freq: Optional[str]) -> Period: ...
     def to_julian_date(self) -> float: ...
     def tz_localize(self, tz: Any = ..., ambigious: Any = ..., nonexistent: Any = ...) -> Timestamp: ...
     def tz_convert(self, tz: Any) -> Timestamp: ...
-    def astimezone(self, tz: Any) -> Timestamp: ...
-    def replace(self, year: OptInt = ..., month: OptInt = ..., day: OptInt = ..., hour: OptInt = ..., minute: OptInt = ..., second: OptInt = ..., microsecond: OptInt = ..., nanosecond: OptInt = ..., tzinfo: Optional[tzinfo] = ..., fold: Fold = ...) -> Timestamp: ...
+    @overload  # type: ignore[override]
+    def __sub__(self, other: datetime) -> Timedelta: ...
+    @overload
+    def __sub__(self, other: timedelta) -> Timestamp: ...
+    def __add__(self, other: timedelta) -> Timestamp: ...
+    if sys.version_info >= (3, 8):
+        def astimezone(self: _S, tz: Optional[tzinfo] = ...) -> _S: ...
+    else:
+        def astimezone(self, tz: Optional[tzinfo] = ...) -> datetime: ...
+    # This is correct. Typeshed doesn't include Optionals, or the Literal correctly
+    def replace(self, year: OptInt = ..., month: OptInt = ..., # type: ignore[override]
+                day: OptInt = ..., hour: OptInt = ..., minute: OptInt = ...,
+                second: OptInt = ..., microsecond: OptInt = ..., nanosecond: OptInt = ...,
+                tzinfo: Optional[tzinfo] = ..., *, fold: Fold = ...) -> datetime: ...
     def round(self, freq: str, ambiguous: Any = ..., nonexistent: Any = ...) -> Timestamp: ...
-    def ceil(self, freq: str, ambiguous: Any = ...,nonexistent: Any = ...) -> Timestamp: ...
-    def floor(self, freq: str, ambiguous: Any = ...,nonexistent: Any = ...) -> Timestamp: ...
-    def isoformat(self, sep: str = ...) -> str: ...
+    def ceil(self, freq: str, ambiguous: Any = ..., nonexistent: Any = ...) -> Timestamp: ...
+    def floor(self, freq: str, ambiguous: Any = ..., nonexistent: Any = ...) -> Timestamp: ...
+    def isoformat(self, sep: str = ..., timespec: str = ...) -> str: ...
     def day_name(self, locale: Optional[str]) -> str: ...
     def month_name(self, locale: Optional[str]) -> str: ...
     def normalize(self) -> Timestamp: ...
     def strftime(self, format: str) -> str: ...
-    def date(self) -> date: ...
-
+    def date(self) -> _date: ...
     @classmethod
     def utcnow(cls) -> Timestamp: ...
     @classmethod
-    def utcfromtimestamp(cls, ts: Timestamp) -> Timestamp: ...
+    def utcfromtimestamp(cls, ts: float) -> Timestamp: ...
+    # Pandas doesn't accept timezone here, unlike datetime
     @classmethod
-    def fromtimestamp(cls, ts: Timestamp) -> Timestamp: ...
+    def fromtimestamp(cls: Type[_S], t: float) -> _S: ... # type: ignore[override]
     @classmethod
-    def combine(cls, date: Any, time: Any) -> Timestamp: ...
+    def combine(cls, date: _date, time: time, tzinfo: Optional[tzinfo] = ...) -> Timestamp: ...
     @classmethod
     def now(cls, tz: Optional[Any] = ...) -> Timestamp: ...
     @classmethod