REF: de-special-case Block._maybe_downcast (#44205)

Author: jbrockmendel

pandas/core/internals/blocks.py

@@ -510,54 +510,24 @@ def _maybe_downcast(self, blocks: list[Block], downcast=None) -> list[Block]:
  [blk.convert(datetime=True, numeric=False) for blk in blocks]
  )
 
- # no need to downcast our float
- # unless indicated
- if downcast is None and self.dtype.kind in ["f", "c", "m", "M"]:
- # passing "infer" to maybe_downcast_to_dtype (via self.downcast)
- #  would be a no-op, so we can short-circuit
+ if downcast is None:
+  return blocks
+ if downcast is False:
+ # turn if off completely
+ # TODO: not reached, deprecate in favor of downcast=None
  return blocks
 
- return extend_blocks([b.downcast(downcast) for b in blocks])
+ return extend_blocks([b._downcast_2d(downcast) for b in blocks])
 
  @final
- def downcast(self, dtypes=None) -> list[Block]:
- """try to downcast each item to the dict of dtypes if present"""
- # turn it off completely
- if dtypes is False:
- return [self]
-
- values = self.values
-
- if self.ndim == 1:
-
- # try to cast all non-floats here
- if dtypes is None:
- dtypes = "infer"
-
- nv = maybe_downcast_to_dtype(values, dtypes)
- return [self.make_block(nv)]
-
- # ndim > 1
- if dtypes is None:
- return [self]
-
- if not (dtypes == "infer" or isinstance(dtypes, dict)):
- raise ValueError(
- "downcast must have a dictionary or 'infer' as its argument"
- )
- elif dtypes != "infer":
- raise AssertionError("dtypes as dict is not supported yet")
-
- return self._downcast_2d()
-
  @maybe_split
- def _downcast_2d(self) -> list[Block]:
+ def _downcast_2d(self, dtype) -> list[Block]:
  """
  downcast specialized to 2D case post-validation.
 
  Refactored to allow use of maybe_split.
  """
- new_values = maybe_downcast_to_dtype(self.values, dtype="infer")
+ new_values = maybe_downcast_to_dtype(self.values, dtype=dtype)
  return [self.make_block(new_values)]
 
  @final
@@ -1098,8 +1068,8 @@ def interpolate(
  **kwargs,
  )
 
- nbs = [self.make_block_same_class(interp_values)]
- return self._maybe_downcast(nbs, downcast)
+ nb = self.make_block_same_class(interp_values)
+ return nb._maybe_downcast([nb], downcast)
 
  def take_nd(
  self,