TYP: Add Literal annotations to TimeGrouper

This doesn't affect the behaviour, since the possible values are already restricted a few lines above this.

Author: NickCrews

pandas/core/resample.py

@@ -1470,14 +1470,14 @@ def __init__(
  self,
  freq="Min",
  closed: Literal["left", "right"] | None = None,
- label: str | None = None,
+ label: Literal["left", "right"] | None = None,
  how="mean",
  axis=0,
  fill_method=None,
  limit=None,
  loffset=None,
  kind: str | None = None,
- convention: str | None = None,
+ convention: Literal["start", "end", "e", "s"] | None = None,
  base: int | None = None,
  origin: str | TimestampConvertibleTypes = "start_day",
  offset: TimedeltaConvertibleTypes | None = None,
@@ -1523,10 +1523,7 @@ def __init__(
  self.closed = closed
  self.label = label
  self.kind = kind
-
- self.convention = convention or "E"
- self.convention = self.convention.lower()
-
+ self.convention = convention if convention is not None else "e"
  self.how = how
  self.fill_method = fill_method
  self.limit = limit