Error on merge function of pandas data frames

[lrob]

Hi,
I'm using pyright in combination with the stubs provided by data-science-types. I'm getting a problem when I check the following code:

import pandas as pd

d = {'a': [1, 2]}
df = pd.DataFrame(data=d)

df_merged: pd.DataFrame = df.merge(right=df)

By running pyright against this code I get the following errors:

 3:19 - error: Argument of type "Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[int]]" cannot be assigned to parameter "data" of type "Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[TypeVar('_T_co')] | DataFrame | Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[TypeVar('_T_co')]] | None" in function "__init__"
  Type "Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[int]]" cannot be assigned to type "Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[TypeVar('_T_co')] | DataFrame | Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[TypeVar('_T_co')]] | None"
    "Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[int]]" is incompatible with "Series[TypeVar('_DType')]"
    "Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[int]]" is incompatible with "Index[TypeVar('_T')]"
    "Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[int]]" is incompatible with "ndarray[TypeVar('_DType')]"
    "Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[int]]" is incompatible with "Sequence[TypeVar('_T_co')]"
    "Dict[_str, Series[TypeVar('_DType')] | Index[TypeVar('_T')] | ndarray[TypeVar('_DType')] | Sequence[int]]" is incompatible with "DataFrame"
    Cannot assign to "None"
      TypeVar "_VT" is invariant
... (reportGeneralTypeIssues)
  4:13 - error: "df.merge(right=df)" has type "Series[Unknown]" and is not callable (reportGeneralTypeIssues)
  4:1 - error: Type of "df_merged" is unknown (reportUnknownVariableType)

Ignoring error 3.19 (that however is not clear to me as well), I would like to focus on error 4:13. Why the function merge is said to have type Series[Unknown]?

To Reproduce
install data-science-types stubs:
pip install data-science-types

install pyright:
sudo npm install -g pyright

run the file with the above code:
pyright test.py

Note that I have enabled the option reportUnknownVariableType

[erictraut]

This is the correct behavior from the perspective of a type checker.

The expression df.merge(right=df) has the type Series[Unknown] because the DataFrame class has no merge method defined, but it does have a __getattr__ method defined, and it returns type Series.

I don't know enough about pandas to offer an informed workaround or recommended bug fix, but you may want to report the issue within the data-science-types repo. I can assure you that Pyright is doing the right thing based on the information it's provided in these stubs.

[lrob]

I'll report it to data-science-types as you suggest.

Thanks for your support