`Series.astype(object)` not supported anymore

[tcrasset]

Describe the bug

Series.astype(object) runs fine, and used to typecheck properly before, but since updating mypy and/or pandas-stubs, it doesn't anymore. Didn't take the time to find a working version that did not throw errors.

To Reproduce

import pandas as pd

s = pd.Series([1, 1])
s = s.astype(object)

Getting the following error message:

error: Argument 1 to "astype" of "Series" has incompatible type "Type[object]"; expected "Union[Type[bool], BooleanDtype, Type[bool_], Literal['bool', 'boolean']]"  [arg-type]
    s = s.astype(object)

Please complete the following information:

• OS: Ubuntu 20.04.5, uname -a yields: Linux REDACTED 5.14.0-1058-oem #66-Ubuntu SMP Fri Feb 10 09:46:18 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

• python version = 3.9.5

• version of type checker: mypy=1.0.1

• version of installed pandas-stubs: pandas_stubs=1.5.3.230304

[tcrasset]

Seems to be causing the issue with DataFrame too:

import pandas as pd

df = pd.DataFrame([1, 1])
df = df.astype(object)

yields

error: Argument 1 to "astype" of "DataFrame" has incompatible type "Type[object]"; expected "Union[Union[Union[Type[bool], BooleanDtype, Type[bool_], Literal['bool', 'boolean']], Union[Type[int], Int8Dtype, Int16Dtype, Int32Dtype, Int64Dtype, Type[signedinteger[Any]], Type[signedinteger[_8Bit]], Type[signedinteger[_16Bit]], Type[signedinteger[_32Bit]], Type[signedinteger[_64Bit]], Type[signedinteger[Any]], Type[unsignedinteger[Any]], Type[unsignedinteger[_8Bit]], Type[unsignedinteger[_16Bit]], Type[unsignedinteger[_32Bit]], Type[unsignedinteger[_64Bit]], Type[unsignedinteger[Any]], Literal['int', 'Int8', 'Int16', 'Int32', 'Int64', 'byte', 'int8', 'int16', 'int32', 'int64', 'intp', 'ubyte', 'uint8', 'uint16', 'uint32', 'uint64', 'uintp']], Union[Type[str], StringDtype, Literal['str', 'string']], Type[bytes], Union[Type[float], Float32Dtype, Float64Dtype, Type[floating[_16Bit]], Type[floating[_32Bit]], Type[floating[_64Bit]], Literal['float', 'Float32', 'Float64', 'float16', 'float32', 'float64']], Union[Type[complex], Type[complexfloating[_32Bit, _32Bit]], Type[complexfloating[_64Bit, _64Bit]], Literal['complex', 'complex64', 'complex128']], Literal['timedelta64[Y]', 'timedelta64[M]', 'timedelta64[W]', 'timedelta64[D]', 'timedelta64[h]', 'timedelta64[m]', 'timedelta64[s]', 'timedelta64[ms]', 'timedelta64[us]', 'timedelta64[μs]', 'timedelta64[ns]', 'timedelta64[ps]', 'timedelta64[fs]', 'timedelta64[as]'], Literal['datetime64[Y]', 'datetime64[M]', 'datetime64[W]', 'datetime64[D]', 'datetime64[h]', 'datetime64[m]', 'datetime64[s]', 'datetime64[ms]', 'datetime64[us]', 'datetime64[μs]', 'datetime64[ns]', 'datetime64[ps]', 'datetime64[fs]', 'datetime64[as]'], Union[CategoricalDtype, Literal['category']], ExtensionDtype], Mapping[Any, Union[ExtensionDtype, Union[str, dtype[generic], Type[str], Type[complex], Type[bool], Type[object]]]], Series[Any]]" [arg-type] df = df.astype(object)

but I see that Type[object] is present in the error message: Mapping[Any, Union[ExtensionDtype, Union[str, dtype[generic], Type[str], Type[complex], Type[bool], Type[object]]]], which would indicate that

df.astype({col: object}) should work. EDIT: It does.

[Dr-Irv]

Thanks for the report. We just introduced making astype() accept specific types and mapping that to different generic Series types.

We need to add object as a valid type here:

pandas-stubs/pandas-stubs/core/series.pyi

Line 1121 in 6829a99

dtype: ExtensionDtype,

and here:

pandas-stubs/pandas-stubs/_typing.pyi

Line 194 in 6829a99

| ExtensionDtype

Tagging @ramvikrams to do this and add appropriate test.

[ramvikrams]

Tagging @ramvikrams to do this and add appropriate test.

Thanks I'll do the change