(fix) 3351 fixes default type var (#3373)

* tests minimal typing extensions in alpine docker

* keeps typevar default but does not use it in the code for backwart compat

deploy/dlt/Dockerfile.minimal

@@ -16,7 +16,7 @@ RUN apk update &&\
     apk add --no-cache ca-certificates curl &&\
     curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py && python3 get-pip.py &&\
     rm get-pip.py &&\
-    pip install --upgrade setuptools wheel pip
+    pip install --upgrade setuptools wheel pip uv
 
 
 # add build labels and envs
@@ -29,28 +29,28 @@ ENV IMAGE_VERSION=${IMAGE_VERSION}
 
 # install exactly the same version of the library we used to build
 COPY dist/dlt-${IMAGE_VERSION}.tar.gz .
-RUN pip install /tmp/pydlt/dlt-${IMAGE_VERSION}.tar.gz
 
 # create app dir to run simple test
 RUN mkdir -p /app
 WORKDIR /app
+RUN uv venv && uv pip install /tmp/pydlt/dlt-${IMAGE_VERSION}.tar.gz --resolution lowest-direct && uv pip install typing-extensions==4.8.0
 RUN rm -r /tmp/pydlt
 
 # make sure dlt can be actually imported
-RUN python -c 'import dlt;import pendulum;'
+RUN uv run python -c 'import dlt;import pendulum;'
 
 # check excluded imports
 COPY deploy/dlt/restrict_imports.py .
-RUN python restrict_imports.py
+RUN uv run python restrict_imports.py
 
 # run simple pipeline
 COPY deploy/dlt/minimal_pipeline.py .
-RUN python minimal_pipeline.py
-RUN dlt pipeline fruit_pipeline info
+RUN uv run python minimal_pipeline.py
+RUN uv run dlt pipeline fruit_pipeline info
 
 # enable workspace
 RUN mkdir -p .dlt && touch .dlt/.workspace
 # RUN dlt pipeline fruit_pipeline info
-RUN dlt workspace info
-RUN python minimal_pipeline.py
-RUN dlt pipeline fruit_pipeline info
+RUN uv run dlt workspace info
+RUN uv run python minimal_pipeline.py
+RUN uv run dlt pipeline fruit_pipeline info

dlt/destinations/impl/databricks/databricks.py

@@ -80,7 +80,7 @@ class DatabricksLoadJob(RunnableLoadJob, HasFollowupJobs):
                 backend.staging_allowed_local_path = file_dir
             else:
                 # thrift backend discontinued on newer databricks connector clients
-                conn_.staging_allowed_local_path = file_dir
+                conn_.staging_allowed_local_path = file_dir  # type: ignore[attr-defined,unused-ignore]
             # local file by uploading to a temporary volume on Databricks
             from_clause, file_name, volume_path, volume_file_path = self._handle_local_file_upload(
                 self._file_path

dlt/extract/items_transform.py

@@ -73,7 +73,7 @@ class ItemTransform(BaseItemTransform[TCustomMetrics], ABC, Generic[TAny, TCusto
         pass
 
 
-class FilterItem(ItemTransform[bool]):
+class FilterItem(ItemTransform[bool, Dict[str, Any]]):
     # mypy needs those to type correctly
     _f_meta: ItemTransformFunctionWithMeta[bool]
     _f: ItemTransformFunctionNoMeta[bool]
@@ -99,7 +99,7 @@ class FilterItem(ItemTransform[bool]):
                 return item if self._f(item) else None
 
 
-class MapItem(ItemTransform[TDataItem]):
+class MapItem(ItemTransform[TDataItem, Dict[str, Any]]):
     # mypy needs those to type correctly
     _f_meta: ItemTransformFunctionWithMeta[TDataItem]
     _f: ItemTransformFunctionNoMeta[TDataItem]
@@ -121,7 +121,7 @@ class MapItem(ItemTransform[TDataItem]):
                 return self._f(item)
 
 
-class YieldMapItem(ItemTransform[Iterator[TDataItem]]):
+class YieldMapItem(ItemTransform[Iterator[TDataItem], Dict[str, Any]]):
     # mypy needs those to type correctly
     _f_meta: ItemTransformFunctionWithMeta[TDataItem]
     _f: ItemTransformFunctionNoMeta[TDataItem]
@@ -144,7 +144,7 @@ class YieldMapItem(ItemTransform[Iterator[TDataItem]]):
                 yield from self._f(item)
 
 
-class ValidateItem(ItemTransform[TDataItem]):
+class ValidateItem(ItemTransform[TDataItem, Dict[str, Any]]):
     """Base class for validators of data items.
 
     Subclass should implement the `__call__` method to either return the data item(s) or raise `extract.exceptions.ValidationError`.
@@ -160,7 +160,7 @@ class ValidateItem(ItemTransform[TDataItem]):
         return self
 
 
-class LimitItem(ItemTransform[TDataItem]):
+class LimitItem(ItemTransform[TDataItem, Dict[str, Any]]):
     placement_affinity: ClassVar[float] = 1.1  # stick to end right behind incremental
 
     def __init__(
@@ -227,7 +227,7 @@ class LimitItem(ItemTransform[TDataItem]):
         return item
 
 
-class MetricsItem(ItemTransform[None]):
+class MetricsItem(ItemTransform[None, Dict[str, Any]]):
     """Collects custom metrics from data flowing through the pipe without modifying items.
 
     The metrics function receives items, optionally meta, and a metrics dictionary that it can

tests/extract/test_decorators.py

@@ -4,7 +4,6 @@ import os
 from typing import Awaitable, Callable, List, Optional, Dict, Iterator, Any, cast
 
 import pytest
-from pydantic import BaseModel
 
 import dlt
 from dlt.common.configuration import known_sections
@@ -386,6 +385,8 @@ def test_nested_hints_decorator() -> None:
 
 
 def test_columns_from_pydantic() -> None:
+    from pydantic import BaseModel
+
     class Columns(BaseModel):
         tags: List[str]
         name: Optional[str]