TYP: Add return types to some top-level func (#30565)

Author: topper-123

pandas/core/indexes/datetimes.py

@@ -1356,7 +1356,7 @@ def date_range(
  name=None,
  closed=None,
  **kwargs,
-):
+) -> DatetimeIndex:
  """
  Return a fixed frequency DatetimeIndex.
 
@@ -1522,7 +1522,7 @@ def bdate_range(
  holidays=None,
  closed=None,
  **kwargs,
-):
+) -> DatetimeIndex:
  """
  Return a fixed frequency DatetimeIndex, with business day as the default
  frequency.

pandas/core/reshape/merge.py

@@ -68,7 +68,7 @@ def merge(
  copy: bool = True,
  indicator: bool = False,
  validate=None,
-):
+) -> "DataFrame":
  op = _MergeOperation(
  left,
  right,
@@ -183,7 +183,7 @@ def merge_ordered(
  fill_method=None,
  suffixes=("_x", "_y"),
  how: str = "outer",
-):
+) -> "DataFrame":
  """
  Perform merge with optional filling/interpolation.
 
@@ -317,7 +317,7 @@ def merge_asof(
  tolerance=None,
  allow_exact_matches: bool = True,
  direction: str = "backward",
-):
+) -> "DataFrame":
  """
  Perform an asof merge. This is similar to a left-join except that we
  match on nearest key rather than equal keys.

pandas/core/reshape/pivot.py

@@ -35,7 +35,7 @@ def pivot_table(
  dropna=True,
  margins_name="All",
  observed=False,
-):
+) -> "DataFrame":
  index = _convert_by(index)
  columns = _convert_by(columns)
 
@@ -148,7 +148,9 @@ def pivot_table(
  table = table.sort_index(axis=1)
 
  if fill_value is not None:
- table = table.fillna(value=fill_value, downcast="infer")
+ filled = table.fillna(value=fill_value, downcast="infer")
+ assert filled is not None # needed for mypy
+ table = filled
 
  if margins:
  if dropna:
@@ -426,7 +428,7 @@ def _convert_by(by):
 
 @Substitution("\ndata : DataFrame")
 @Appender(_shared_docs["pivot"], indents=1)
-def pivot(data: "DataFrame", index=None, columns=None, values=None):
+def pivot(data: "DataFrame", index=None, columns=None, values=None) -> "DataFrame":
  if values is None:
  cols = [columns] if index is None else [index, columns]
  append = index is None

pandas/io/json/_normalize.py

@@ -118,7 +118,7 @@ def _json_normalize(
  errors: Optional[str] = "raise",
  sep: str = ".",
  max_level: Optional[int] = None,
-):
+) -> "DataFrame":
  """
  Normalize semi-structured JSON data into a flat table.