diff --git a/python/docs/source/examples/bluesky.py b/python/docs/source/examples/bluesky.py
index 316a34d31..c260fc960 100644
--- a/python/docs/source/examples/bluesky.py
+++ b/python/docs/source/examples/bluesky.py
@@ -113,7 +113,7 @@ async def receive_outputs():
 
 
 # Copied from https://raw.githubusercontent.com/MarshalX/atproto/main/examples/firehose/process_commits.py
-def _get_ops_by_type(
+def _get_ops_by_type(  # noqa: C901, E302
     commit: models.ComAtprotoSyncSubscribeRepos.Commit,
 ) -> dict:  # noqa: C901, E302
     operation_by_type = {
diff --git a/python/mypy.ini b/python/mypy.ini
index 07bbced46..dcbe5289f 100644
--- a/python/mypy.ini
+++ b/python/mypy.ini
@@ -12,4 +12,7 @@ ignore_missing_imports = True
 ignore_missing_imports = True
 
 [mypy-plotly.*]
+ignore_missing_imports = True
+
+[mypy-graphviz.*]
 ignore_missing_imports = True
\ No newline at end of file
diff --git a/python/poetry.lock b/python/poetry.lock
index a7e817d55..7a7417640 100644
--- a/python/poetry.lock
+++ b/python/poetry.lock
@@ -722,7 +722,7 @@ develop = ["build", "twine"]
 name = "graphviz"
 version = "0.20.1"
 description = "Simple Python interface for Graphviz"
-optional = true
+optional = false
 python-versions = ">=3.7"
 files = [
     {file = "graphviz-0.20.1-py3-none-any.whl", hash = "sha256:587c58a223b51611c0cf461132da386edd896a029524ca61a1462b880bf97977"},
@@ -3491,9 +3491,10 @@ docs = ["furo", "jaraco.packaging (>=9.3)", "jaraco.tidelift (>=1.4)", "rst.link
 testing = ["big-O", "jaraco.functools", "jaraco.itertools", "more-itertools", "pytest (>=6)", "pytest-black (>=0.3.7)", "pytest-checkdocs (>=2.4)", "pytest-cov", "pytest-enabler (>=2.2)", "pytest-ignore-flaky", "pytest-mypy (>=0.9.1)", "pytest-ruff"]
 
 [extras]
+explain = ["graphviz"]
 plot = ["plotly"]
 
 [metadata]
 lock-version = "2.0"
 python-versions = ">=3.9,<4.0"
-content-hash = "d8a73b55ee47f657e4f7d51184206b4049c23c70ce517766da7238f16aeb2511"
+content-hash = "a690c5a87f12c8dd5dcd1842a32acd3e79b090cc5fc5ccb2ed7e184eafdc644e"
diff --git a/python/pyproject.toml b/python/pyproject.toml
index a20f6c00c..57fd4fef3 100644
--- a/python/pyproject.toml
+++ b/python/pyproject.toml
@@ -41,6 +41,7 @@ plotly = {version = "^5.16.1", optional = true}
 
 [tool.poetry.extras]
 plot = ["plotly"]
+explain = ["graphviz"]
 
 [tool.poetry.group.dev.dependencies]
 # Dependencies for building and developing.
@@ -61,6 +62,7 @@ pep8-naming = ">=0.12.1"
 pydocstyle = "^6.3.0"
 pyupgrade = ">=2.29.1"
 autoflake = "^2.2.0"
+graphviz = { version = "^0.20.1" }
 
 [tool.poetry.group.safety]
 optional = true
@@ -76,6 +78,7 @@ optional = true
 mypy = ">=0.930"
 pandas-stubs = "^2.0.2"
 typeguard = ">=2.13.3"
+graphviz = { version = "^0.20.1" }
 
 [tool.poetry.group.docs]
 # Dependencies for documentation.
diff --git a/python/pysrc/kaskada/_timestream.py b/python/pysrc/kaskada/_timestream.py
index efcf6fb84..197689223 100644
--- a/python/pysrc/kaskada/_timestream.py
+++ b/python/pysrc/kaskada/_timestream.py
@@ -6,6 +6,7 @@
 import warnings
 from datetime import datetime, timedelta
 from typing import (
+    TYPE_CHECKING,
     Callable,
     List,
     Literal,
@@ -27,6 +28,9 @@
 from ._execution import Execution, ResultIterator, _ExecutionOptions
 
 
+if TYPE_CHECKING:
+    import graphviz
+
 #: A literal value that can be used as an argument to a Timestream operation.
 LiteralValue: TypeAlias = Optional[Union[int, str, float, bool, timedelta, datetime]]
 
@@ -1199,7 +1203,7 @@ def explain(
         kind: Literal["initial_dfg", "final_dfg", "final_plan"] = "final_plan",
         results: Optional[Union[kd.results.History, kd.results.Snapshot]] = None,
         mode: Literal["once", "live"] = "once",
-    ) -> Union[str, "graphviz.Source"]:
+    ) -> "graphviz.Source":
         """Return an explanation of this Timestream will be executed.
 
         This is intended for understanding how a given Timestream query will
@@ -1212,6 +1216,7 @@ def explain(
             mode: The execution mode to use. Defaults to `'once'` to produce the results
               from the currently available data. Use `'live'` to start a standing query
               that continues to process new data until stopped.
+
         Returns:
             A GraphViz representation of the execution plan as a string, SVG string, or SVG.
             Specific representation depends on the `format` argument.
@@ -1223,6 +1228,8 @@ def explain(
             This method is intended for debugging and development purposes only.
             The API may change in the future.
         """
+        import graphviz
+
         expr = self
         if not pa.types.is_struct(self.data_type):
             # The execution engine requires a struct, so wrap this in a record.
@@ -1232,17 +1239,9 @@ def explain(
             results, row_limit=None, max_batch_size=None, mode=mode
         )
 
-        dot = expr._ffi_expr.plan(kind, options)
-        try:
-            import graphviz
-
-            dot = graphviz.Source(dot, engine="dot")
-            return dot
-        except ImportError:
-            raise ValueError(
-                "`explain` requires `graphviz` python package: "
-                "install it using pip (or install `kaskada[explain]`)"
-            ) from None
+        dot = expr._ffi_expr.explain(kind, options)
+        dot = graphviz.Source(dot, engine="dot")
+        return dot
 
     def _execute(
         self,
diff --git a/python/pysrc/kaskada/sources/arrow.py b/python/pysrc/kaskada/sources/arrow.py
index 41a452e33..3d053e484 100644
--- a/python/pysrc/kaskada/sources/arrow.py
+++ b/python/pysrc/kaskada/sources/arrow.py
@@ -160,6 +160,7 @@ async def create(
         """Create a source reading from rows represented as dicts.
 
         Args:
+            rows: The input row(s) as a dictionary or list of dictionaries.
             time_column: The name of the column containing the time.
             key_column: The name of the column containing the key.
             queryable: Whether added rows will be available for running queries.