CLN: Add typing for dtype argument in io directory (GH38808)

pandas/io/excel/_base.py

@@ -12,7 +12,7 @@
 from pandas._config import config
 
 from pandas._libs.parsers import STR_NA_VALUES
-from pandas._typing import Buffer, FilePathOrBuffer, StorageOptions
+from pandas._typing import Buffer, DtypeArg, FilePathOrBuffer, StorageOptions
 from pandas.compat._optional import import_optional_dependency
 from pandas.errors import EmptyDataError
 from pandas.util._decorators import Appender, deprecate_nonkeyword_arguments, doc
@@ -309,7 +309,7 @@ def read_excel(
     index_col=None,
     usecols=None,
     squeeze=False,
-    dtype=None,
+    dtype: Optional[DtypeArg] = None,
     engine=None,
     converters=None,
     true_values=None,
@@ -433,7 +433,7 @@ def parse(
         index_col=None,
         usecols=None,
         squeeze=False,
-        dtype=None,
+        dtype: Optional[DtypeArg] = None,
         true_values=None,
         false_values=None,
         skiprows=None,

pandas/io/json/_json.py

@@ -11,6 +11,8 @@
 from pandas._libs.tslibs import iNaT
 from pandas._typing import (
     CompressionOptions,
+    DtypeArg,
+    FrameOrSeriesUnion,
     IndexLabel,
     JSONSerializable,
     StorageOptions,
@@ -296,7 +298,7 @@ def read_json(
     path_or_buf=None,
     orient=None,
     typ="frame",
-    dtype=None,
+    dtype: Optional[DtypeArg] = None,
     convert_axes=None,
     convert_dates=True,
     keep_default_dates: bool = True,
@@ -775,7 +777,7 @@ def __init__(
         self,
         json,
         orient,
-        dtype=None,
+        dtype: Optional[DtypeArg] = None,
         convert_axes=True,
         convert_dates=True,
         keep_default_dates=False,
@@ -809,7 +811,7 @@ def __init__(
         self.convert_dates = convert_dates
         self.date_unit = date_unit
         self.keep_default_dates = keep_default_dates
-        self.obj = None
+        self.obj: Optional[FrameOrSeriesUnion] = None
 
     def check_keys_split(self, decoded):
         """

pandas/io/parsers.py

@@ -31,7 +31,7 @@
 import pandas._libs.parsers as parsers
 from pandas._libs.parsers import STR_NA_VALUES
 from pandas._libs.tslibs import parsing
-from pandas._typing import FilePathOrBuffer, StorageOptions, Union
+from pandas._typing import DtypeArg, FilePathOrBuffer, StorageOptions, Union
 from pandas.errors import (
     AbstractMethodError,
     EmptyDataError,
@@ -546,7 +546,7 @@ def read_csv(
     prefix=None,
     mangle_dupe_cols=True,
     # General Parsing Configuration
-    dtype=None,
+    dtype: Optional[DtypeArg] = None,
     engine=None,
     converters=None,
     true_values=None,
@@ -626,7 +626,7 @@ def read_table(
     prefix=None,
     mangle_dupe_cols=True,
     # General Parsing Configuration
-    dtype=None,
+    dtype: Optional[DtypeArg] = None,
     engine=None,
     converters=None,
     true_values=None,
@@ -3502,25 +3502,22 @@ def _clean_index_names(columns, index_col, unnamed_cols):
     return index_names, columns, index_col
 
 
-def _get_empty_meta(columns, index_col, index_names, dtype=None):
+def _get_empty_meta(columns, index_col, index_names, dtype: Optional[DtypeArg] = None):
     columns = list(columns)
 
     # Convert `dtype` to a defaultdict of some kind.
     # This will enable us to write `dtype[col_name]`
     # without worrying about KeyError issues later on.
-    if not isinstance(dtype, dict):
+    if not is_dict_like(dtype):
         # if dtype == None, default will be object.
         default_dtype = dtype or object
         dtype = defaultdict(lambda: default_dtype)
     else:
-        # Save a copy of the dictionary.
-        _dtype = dtype.copy()
-        dtype = defaultdict(lambda: object)
-
-        # Convert column indexes to column names.
-        for k, v in _dtype.items():
-            col = columns[k] if is_integer(k) else k
-            dtype[col] = v
+        dtype = cast(dict, dtype)
+        dtype = defaultdict(
+            lambda: object,
+            {columns[k] if is_integer(k) else k: v for k, v in dtype.items()},
+        )
 
     # Even though we have no data, the "index" of the empty DataFrame
     # could for example still be an empty MultiIndex. Thus, we need to

pandas/io/pytables.py

@@ -29,7 +29,14 @@
 
 from pandas._libs import lib, writers as libwriters
 from pandas._libs.tslibs import timezones
-from pandas._typing import ArrayLike, FrameOrSeries, FrameOrSeriesUnion, Label, Shape
+from pandas._typing import (
+    ArrayLike,
+    DtypeArg,
+    FrameOrSeries,
+    FrameOrSeriesUnion,
+    Label,
+    Shape,
+)
 from pandas.compat._optional import import_optional_dependency
 from pandas.compat.pickle_compat import patch_pickle
 from pandas.errors import PerformanceWarning
@@ -2259,7 +2266,7 @@ def __init__(
         table=None,
         meta=None,
         metadata=None,
-        dtype=None,
+        dtype: Optional[DtypeArg] = None,
         data=None,
     ):
         super().__init__(