SNOW-874658: Type hints for execute and executemany in DictCursor is incorrect

[recrsn]

Python version

Python 3.9.17

Operating system and processor architecture

macOS-13.4.1-arm64-arm-64bit

Installed packages

asn1crypto==1.5.1
certifi==2023.5.7
cffi==1.15.1
charset-normalizer==3.1.0
cryptography==40.0.2
filelock==3.12.0
idna==3.4
oscrypto==1.3.0
packaging==23.1
pycparser==2.21
pycryptodomex==3.18.0
PyJWT==2.7.0
pyOpenSSL==23.1.1
pytz==2023.3
requests==2.31.0
snowflake-connector-python==3.0.4
sortedcontainers==2.4.0
typing_extensions==4.6.0
urllib3==1.26.16

What did you do?

# Write some code using execute or executemany and run mypy
#
# Like 


connection = snowflake.connector.connect(...)
with connection.cursor(DictCursor) as cur: # issue here too, as cursor always returns a SnowflakeCursor, this should be generified
    cur.execute("SELECT c1,c2 FROM example")
    results = cur.fetchall()
    for row in results:
       c1 = row["C1"] # error here, as SnowflakeCursor marks return type as list


# The issue stems from DictCursor not defining overrides correctly.

What did you expect to see?

No mypy errors

Can you set logging to DEBUG and collect the logs?

No response

[lokucrazy]

howdy, having a similar problem with mypy and snowflake-connector-python, ended up doing this redundant casting to appease mypy

cursor = connection.cursor(DictCursor)
cursor.execute(SQL)
result = cursor.fetchone()
r_dict = dict(result) if result and isinstance(result, dict) else None
if r_dict:
        return r_dict["Col"]

this was the error messages I would get with mypy

error: No overload variant of "__getitem__" of "tuple" matches argument type "str"  [call-overload]
note: Possible overload variants:
note:     def __getitem__(self, SupportsIndex, /) -> Any
note:     def __getitem__(self, slice, /) -> tuple[Any, ...]
error: Value of type "dict[Any, Any] | tuple[Any, ...] | None" is not indexable  [index]

So yeah the issue for me is that we can't specify with DictCursor that the internal _result field is going to be a dictionary. Is this getting worked on?

[sfc-gh-dszmolka]

hi and thank you for raising this ! i understand this is still an issue and definitely needs to be addressed somehow. we'll take a look and I'll keep this thread posted with new information.