diff --git a/src/ipyforcegraph/_base.py b/src/ipyforcegraph/_base.py
index 0acb213..08e9597 100644
--- a/src/ipyforcegraph/_base.py
+++ b/src/ipyforcegraph/_base.py
@@ -3,18 +3,22 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
+from typing import TYPE_CHECKING
+
 import ipywidgets as W
 import traitlets as T
 
-from . import _types as _t
 from .constants import EXTENSION_NAME, EXTENSION_SPEC_VERSION
 
+if TYPE_CHECKING:
+    from . import _types as _t
+
 
 class ForceBase(W.Widget):
     """The base class for all ``IPyForceGraph`` widgets."""
 
-    _model_name: _t.Tstr = T.Unicode("ForceBaseModel").tag(sync=True)
-    _model_module: _t.Tstr = T.Unicode(EXTENSION_NAME).tag(sync=True)
-    _model_module_version: _t.Tstr = T.Unicode(EXTENSION_SPEC_VERSION).tag(sync=True)
-    _view_module: _t.Tstr = T.Unicode(EXTENSION_NAME).tag(sync=True)
-    _view_module_version: _t.Tstr = T.Unicode(EXTENSION_SPEC_VERSION).tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ForceBaseModel").tag(sync=True)
+    _model_module: "_t.Tstr" = T.Unicode(EXTENSION_NAME).tag(sync=True)
+    _model_module_version: "_t.Tstr" = T.Unicode(EXTENSION_SPEC_VERSION).tag(sync=True)
+    _view_module: "_t.Tstr" = T.Unicode(EXTENSION_NAME).tag(sync=True)
+    _view_module_version: "_t.Tstr" = T.Unicode(EXTENSION_SPEC_VERSION).tag(sync=True)
diff --git a/src/ipyforcegraph/_types.py b/src/ipyforcegraph/_types.py
index a47d673..a7d8b2c 100644
--- a/src/ipyforcegraph/_types.py
+++ b/src/ipyforcegraph/_types.py
@@ -19,3 +19,5 @@
 Tbool = T.Bool[bool, Union[bool, int]]
 
 Tdict_any = T.Instance[Dict[Any, Any]]
+
+Tenum_str_str = T.Enum[str, str]
diff --git a/src/ipyforcegraph/behaviors/_base.py b/src/ipyforcegraph/behaviors/_base.py
index 1931512..377a232 100644
--- a/src/ipyforcegraph/behaviors/_base.py
+++ b/src/ipyforcegraph/behaviors/_base.py
@@ -3,15 +3,17 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Any, Optional, Union
+from typing import TYPE_CHECKING, Any, Optional, Union
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from .._base import ForceBase
 from ..trait_utils import JSON_TYPES, coerce
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 TFeature = Optional[Union["Column", "Nunjucks", str]]
 TNumFeature = Optional[Union["Column", "Nunjucks", str, int, float]]
 TBoolFeature = Optional[Union["Column", "Nunjucks", str, bool]]
@@ -36,9 +38,9 @@ class DEFAULT_RANK:
 class Behavior(ForceBase):
     """The base class for all IPyForceGraph graph behaviors."""
 
-    _model_name: _t.Tstr = T.Unicode("BehaviorModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("BehaviorModel").tag(sync=True)
 
-    rank: _t.Tint = T.Int(
+    rank: "_t.Tint" = T.Int(
         DEFAULT_RANK.behavior,
         help=("order in which behaviors are applied: lower numbers are applied first."),
     ).tag(sync=True)
@@ -47,8 +49,8 @@ class Behavior(ForceBase):
 class BaseD3Force(Behavior):
     """A base for all ``d3-force-3d`` force wrappers."""
 
-    _model_name: _t.Tstr = T.Unicode("BaseD3ForceModel").tag(sync=True)
-    active: _t.Tbool = T.Bool(True, help="whether the force is currently active").tag(
+    _model_name: "_t.Tstr" = T.Unicode("BaseD3ForceModel").tag(sync=True)
+    active: "_t.Tbool" = T.Bool(True, help="whether the force is currently active").tag(
         sync=True
     )
 
@@ -56,7 +58,7 @@ class BaseD3Force(Behavior):
 class ShapeBase(ForceBase):
     """A base class from which all :mod:`~ipyforcegraph.behaviors.shapes` inherit."""
 
-    _model_name: _t.Tstr = T.Unicode("ShapeBaseModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ShapeBaseModel").tag(sync=True)
 
 
 class DynamicValue(ForceBase):
@@ -66,11 +68,11 @@ class DynamicValue(ForceBase):
 
     JSON_DATA_TYPES = JSON_TYPES.get_supported_types()
 
-    value: _t.Tstr = T.Unicode(
+    value: "_t.Tstr" = T.Unicode(
         "", help="the source used to compute the value for the trait"
     ).tag(sync=True)
 
-    coerce: _t.Tstr_maybe = T.Unicode(
+    coerce: "_t.Tstr_maybe" = T.Unicode(
         help="name of a JSON Schema ``type`` into which to coerce the final value",
         allow_none=True,
     ).tag(sync=True)
@@ -98,7 +100,7 @@ def _validate_coercer(self, proposal: T.Bunch) -> Optional[str]:
 class Column(DynamicValue):
     """A column from a :class:`~ipyforcegraph.sources.dataframe.DataFrameSource`."""
 
-    _model_name: _t.Tstr = T.Unicode("ColumnModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ColumnModel").tag(sync=True)
 
 
 class Nunjucks(DynamicValue):
@@ -141,7 +143,7 @@ class Nunjucks(DynamicValue):
         rgb({{ c }},0,0)
     """
 
-    _model_name: _t.Tstr = T.Unicode("NunjucksModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("NunjucksModel").tag(sync=True)
 
 
 def _make_trait(
@@ -178,7 +180,7 @@ def _make_trait(
 class HasScale(ShapeBase):
     """A shape that has ``scale_on_zoom``."""
 
-    _model_name: _t.Tstr = T.Unicode("HasScaleModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("HasScaleModel").tag(sync=True)
 
     scale_on_zoom: TBoolFeature = _make_trait(
         "whether font size/stroke respects the global scale. Has no impact on `link` shapes.",
@@ -193,7 +195,7 @@ def _validate_scale_bools(self, proposal: T.Bunch) -> Any:
 class HasFillAndStroke(HasScale):
     """A shape that has ``fill`` and ``stroke``."""
 
-    _model_name: _t.Tstr = T.Unicode("HasFillModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("HasFillModel").tag(sync=True)
     fill: TFeature = _make_trait("the fill color of a shape")
     stroke: TFeature = _make_trait("the stroke color of a shape")
     stroke_width: TNumFeature = _make_trait("the stroke width of a shape", numeric=True)
@@ -215,7 +217,7 @@ def _validate_has_fill_and_stroke_arrays(self, proposal: T.Bunch) -> Any:
 class HasOffsets(ShapeBase):
     """A shape that can be offset in the horizontal, vertical, or elevation dimensions."""
 
-    _model_name: _t.Tstr = T.Unicode("HasOffsetsModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("HasOffsetsModel").tag(sync=True)
 
     offset_x: float = _make_trait(
         "the relative horizontal offset from the middle of the shape in ``px``",
@@ -238,7 +240,7 @@ def _validate_offset_numerics(self, proposal: T.Bunch) -> Any:
 class HasDimensions(HasFillAndStroke, HasOffsets):
     """A shape that has ``width``, ``height`` and ``depth``."""
 
-    _model_name: _t.Tstr = T.Unicode("HasDimensionsModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("HasDimensionsModel").tag(sync=True)
 
     width: TNumFeature = _make_trait("the width of a shape in ``px``", numeric=True)
     height: TNumFeature = _make_trait("the height of a shape in ``px``", numeric=True)
diff --git a/src/ipyforcegraph/behaviors/forces.py b/src/ipyforcegraph/behaviors/forces.py
index 3404cea..4a76f78 100644
--- a/src/ipyforcegraph/behaviors/forces.py
+++ b/src/ipyforcegraph/behaviors/forces.py
@@ -10,12 +10,11 @@
 # Distributed under the terms of the Modified BSD License.
 
 import enum
-from typing import Any, Dict, Optional
+from typing import TYPE_CHECKING, Any, Dict, Optional
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from ..trait_utils import JSON_TYPES, coerce, validate_enum
 from ._base import (
     BaseD3Force,
@@ -26,8 +25,10 @@
     _make_trait,
 )
 
-TForceDict = Dict[str, BaseD3Force]
-TForceDictDesc = T.TraitType[Dict[str, BaseD3Force], Dict[str, BaseD3Force]]
+if TYPE_CHECKING:
+    from .. import _types as _t
+
+    TForceDict = Dict[str, BaseD3Force]
 
 
 @W.register
@@ -39,43 +40,45 @@ class GraphForces(Behavior):
     For more, see the frontend documentation on https://github.com/vasturiano/force-graph#force-engine-d3-force-configuration
     """
 
-    _model_name: _t.Tstr = T.Unicode("GraphForcesModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("GraphForcesModel").tag(sync=True)
 
-    forces: TForceDictDesc = T.Dict(
+    forces: "T.TraitType[Dict[str, BaseD3Force], Dict[str, BaseD3Force]]" = T.Dict(
         value_trait=T.Instance(BaseD3Force, allow_none=True),
         help="named forces. Set a name `None` to remove a force: By default, ForceGraph has `link`, `charge`, and `center`",
     ).tag(sync=True, **W.widget_serialization)
 
-    warmup_ticks: _t.Tint = T.Int(
+    warmup_ticks: "_t.Tint" = T.Int(
         0,
         min=0,
         help="layout engine cycles to dry-run at ignition before starting to render",
     ).tag(sync=True)
 
-    cooldown_ticks: _t.Tint = T.Int(
+    cooldown_ticks: "_t.Tint" = T.Int(
         -1,
         help="frames to render before stopping and freezing the layout engine. Values less than zero will be translated to `Infinity`",
     ).tag(sync=True)
 
-    alpha_min: _t.Tfloat = T.Float(
+    alpha_min: "_t.Tfloat" = T.Float(
         0.0, min=0.0, max=1.0, help="simulation alpha min parameter"
     ).tag(sync=True)
 
-    alpha_decay: _t.Tfloat = T.Float(
+    alpha_decay: "_t.Tfloat" = T.Float(
         0.0228,
         min=0.0,
         max=1.0,
         help="simulation intensity decay parameter",
     ).tag(sync=True)
 
-    velocity_decay: _t.Tfloat = T.Float(
+    velocity_decay: "_t.Tfloat" = T.Float(
         0.4,
         min=0.0,
         max=1.0,
         help="nodes' velocity decay that simulates the medium resistance",
     ).tag(sync=True)
 
-    def __init__(self, forces: Optional[TForceDict] = None, *args: Any, **kwargs: Any):
+    def __init__(
+        self, forces: "Optional[TForceDict]" = None, *args: Any, **kwargs: Any
+    ):
         kwargs["forces"] = forces or {}
         super().__init__(*args, **kwargs)
 
@@ -87,7 +90,7 @@ class Link(BaseD3Force):
     https://github.com/d3/d3-force#links
     """
 
-    _model_name: _t.Tstr = T.Unicode("LinkForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("LinkForceModel").tag(sync=True)
 
     distance: TNumFeature = _make_trait(
         "the 'desired' distance of a link. Context takes ``link``", numeric=True
@@ -112,21 +115,21 @@ class Center(BaseD3Force):
     https://github.com/d3/d3-force#centering
     """
 
-    _model_name: _t.Tstr = T.Unicode("CenterForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("CenterForceModel").tag(sync=True)
 
-    x: _t.Tfloat_maybe = T.Float(
+    x: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the x-coordinate of the position to center the nodes on",
     ).tag(sync=True)
 
-    y: _t.Tfloat_maybe = T.Float(
+    y: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the y-coordinate of the position to center the nodes on",
     ).tag(sync=True)
 
-    z: _t.Tfloat_maybe = T.Float(
+    z: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the z-coordinate of the position to center the nodes on (only applies to ``ForceGraph3D``)",
@@ -141,7 +144,7 @@ class X(BaseD3Force):
     https://github.com/d3/d3-force#positioning
     """
 
-    _model_name: _t.Tstr = T.Unicode("XForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("XForceModel").tag(sync=True)
 
     x: TNumFeature = _make_trait(
         "the x-coordinate of the centering position to the specified number. "
@@ -169,7 +172,7 @@ class Y(BaseD3Force):
     https://github.com/d3/d3-force#positioning
     """
 
-    _model_name: _t.Tstr = T.Unicode("YForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("YForceModel").tag(sync=True)
 
     y: TNumFeature = _make_trait(
         "the y-coordinate of the centering position. " "Context takes ``node``.",
@@ -199,7 +202,7 @@ class Z(BaseD3Force):
     https://github.com/d3/d3-force#positioning
     """
 
-    _model_name: _t.Tstr = T.Unicode("ZForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ZForceModel").tag(sync=True)
 
     z: TNumFeature = _make_trait(
         "the z-coordinate of the centering position. Context takes ``node``.",
@@ -230,7 +233,7 @@ class ManyBody(BaseD3Force):
     https://github.com/d3/d3-force#many-body
     """
 
-    _model_name: _t.Tstr = T.Unicode("ManyBodyForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ManyBodyForceModel").tag(sync=True)
 
     strength: TNumFeature = _make_trait(
         "a nunjucks template to use to calculate strength. Context takes ``node``",
@@ -239,19 +242,19 @@ class ManyBody(BaseD3Force):
         allow_none=False,
     )
 
-    theta: _t.Tfloat_maybe = T.Float(
+    theta: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the Barnes-Hut approximation criterion",
     ).tag(sync=True)
 
-    distance_min: _t.Tfloat_maybe = T.Float(
+    distance_min: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the minimum distance between nodes over which this force is considered",
     ).tag(sync=True)
 
-    distance_max: _t.Tfloat_maybe = T.Float(
+    distance_max: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the maximum distance between nodes over which this force is considered",
@@ -270,7 +273,7 @@ class Radial(BaseD3Force):
     https://github.com/d3/d3-force#forceRadial
     """
 
-    _model_name: _t.Tstr = T.Unicode("RadialForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("RadialForceModel").tag(sync=True)
 
     radius: TNumFeature = _make_trait(
         "radius of the force. Context takes ``node``",
@@ -284,19 +287,19 @@ class Radial(BaseD3Force):
         allow_none=False,
     )
 
-    x: _t.Tfloat_maybe = T.Float(
+    x: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the x-coordinate of the centering position",
     ).tag(sync=True)
 
-    y: _t.Tfloat_maybe = T.Float(
+    y: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the y-coordinate of the centering position",
     ).tag(sync=True)
 
-    z: _t.Tfloat_maybe = T.Float(
+    z: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the z-coordinate of the centering position",
@@ -315,14 +318,14 @@ class Collision(BaseD3Force):
     https://github.com/d3/d3-force#collision
     """
 
-    _model_name: _t.Tstr = T.Unicode("CollisionForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("CollisionForceModel").tag(sync=True)
 
     radius: TNumFeature = _make_trait(
         "The radius of collision by node. Context takes ``node``",
         numeric=True,
     )
 
-    strength: _t.Tfloat_maybe = T.Float(
+    strength: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         min=0.0,
@@ -342,9 +345,9 @@ class Cluster(BaseD3Force):
     https://github.com/vasturiano/d3-force-cluster-3d
     """
 
-    _model_name: _t.Tstr = T.Unicode("ClusterForceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ClusterForceModel").tag(sync=True)
 
-    strength: _t.Tfloat_maybe = T.Float(
+    strength: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         min=0.0,
@@ -352,7 +355,7 @@ class Cluster(BaseD3Force):
         help="the strength of the force",
     ).tag(sync=True)
 
-    inertia: _t.Tfloat_maybe = T.Float(
+    inertia: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         min=0.0,
@@ -425,16 +428,16 @@ class Mode(enum.Enum):
         radial_out = "radialout"
         radial_in = "radialin"
 
-    _model_name: _t.Tstr = T.Unicode("DAGBehaviorModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("DAGBehaviorModel").tag(sync=True)
 
-    mode: T.Enum[str, str] = T.Enum(
+    mode: "_t.Tenum_str_str" = T.Enum(
         values=[*[m.value for m in Mode], *Mode],
         help="DAG constraint layout mode/direction",
         default_value=None,
         allow_none=True,
     ).tag(sync=True)
 
-    level_distance: _t.Tfloat_maybe = T.Float(
+    level_distance: "_t.Tfloat_maybe" = T.Float(
         default_value=None,
         help="distance between DAG levels",
         allow_none=True,
diff --git a/src/ipyforcegraph/behaviors/particles.py b/src/ipyforcegraph/behaviors/particles.py
index d88da60..a495ec5 100644
--- a/src/ipyforcegraph/behaviors/particles.py
+++ b/src/ipyforcegraph/behaviors/particles.py
@@ -3,15 +3,17 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Any
+from typing import TYPE_CHECKING, Any
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from ..trait_utils import JSON_TYPES, coerce
 from ._base import Behavior, TFeature, TNumFeature, _make_trait
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 
 @W.register
 class LinkParticles(Behavior):
@@ -22,7 +24,7 @@ class LinkParticles(Behavior):
        or they will exceed the frame rate of the animation.
     """
 
-    _model_name: _t.Tstr = T.Unicode("LinkParticleModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("LinkParticleModel").tag(sync=True)
 
     color: TFeature = _make_trait("the color of the particles")
     density: TNumFeature = _make_trait(
diff --git a/src/ipyforcegraph/behaviors/recording.py b/src/ipyforcegraph/behaviors/recording.py
index c03fdb9..6f90a0c 100644
--- a/src/ipyforcegraph/behaviors/recording.py
+++ b/src/ipyforcegraph/behaviors/recording.py
@@ -3,22 +3,24 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Any, Optional, Tuple
+from typing import TYPE_CHECKING, Any, Optional, Tuple
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from ..sources.dataframe import DataFrameSource
 from ..trait_utils import JSON_TYPES, coerce
 from ._base import Behavior, TFeature, _make_trait
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 
 @W.register
 class GraphImage(Behavior):
     """Captures multiple subsequent frames of a canvas, each as an :class:`~ipywidgets.widgets.widget_media.Image`."""
 
-    _model_name: _t.Tstr = T.Unicode("GraphImageModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("GraphImageModel").tag(sync=True)
 
     capturing = T.Bool(False, help="whether the frame capture is currently active").tag(
         sync=True
@@ -56,9 +58,9 @@ def _on_frame_count(self, change: T.Bunch) -> None:
 class GraphData(Behavior):
     """Captures multiple subsequent ticks of a graph simulation, each as a :class:`~pandas.DataFrame`."""
 
-    _model_name: _t.Tstr = T.Unicode("GraphDataModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("GraphDataModel").tag(sync=True)
 
-    capturing: _t.Tbool = T.Bool(
+    capturing: "_t.Tbool" = T.Bool(
         False, help="whether the dataframe capture is currently active"
     ).tag(sync=True)
 
@@ -92,9 +94,9 @@ def _on_source_count(self, change: T.Bunch) -> None:
 class GraphCamera(Behavior):
     """Captures the current center and zoom of the graph viewport."""
 
-    _model_name: _t.Tstr = T.Unicode("GraphCameraModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("GraphCameraModel").tag(sync=True)
 
-    zoom: _t.Tfloat_maybe = T.Float(
+    zoom: "_t.Tfloat_maybe" = T.Float(
         None, allow_none=True, help="the current 2D zoom level of the viewport"
     ).tag(sync=True)
 
@@ -110,7 +112,7 @@ class GraphCamera(Behavior):
         T.Int(), help="the indices of all visible nodes"
     ).tag(sync=True)
 
-    capturing: _t.Tbool = T.Bool(
+    capturing: "_t.Tbool" = T.Bool(
         False, help="whether visible nodes should be captured as ``visible``"
     ).tag(sync=True)
 
@@ -119,9 +121,9 @@ class GraphCamera(Behavior):
 class GraphDirector(Behavior):
     """Set a desired center and zoom of the graph viewport."""
 
-    _model_name: _t.Tstr = T.Unicode("GraphDirectorModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("GraphDirectorModel").tag(sync=True)
 
-    zoom: _t.Tfloat_maybe = T.Float(
+    zoom: "_t.Tfloat_maybe" = T.Float(
         None, allow_none=True, help="the desired 2D zoom level of the viewport"
     ).tag(sync=True)
 
@@ -131,11 +133,11 @@ class GraphDirector(Behavior):
         help="the desired center of the viewport as `[x, y, z?]`",
     ).tag(sync=True)
 
-    look_at: _t.Tfloat_maybe = W.TypedTuple(
+    look_at: "_t.Tfloat_maybe" = W.TypedTuple(
         T.Float(), allow_none=True, help="the direction of a 3d camera as `[x, y, z]`"
     ).tag(sync=True)
 
-    zoom_first: _t.Tbool = T.Bool(
+    zoom_first: "_t.Tbool" = T.Bool(
         False, help="whether to zoom the viewport before panning"
     ).tag(sync=True)
 
@@ -145,19 +147,19 @@ class GraphDirector(Behavior):
         by_column=True,
     )
 
-    zoom_duration: _t.Tfloat = T.Float(0.2, help="seconds to animate a zoom").tag(
+    zoom_duration: "_t.Tfloat" = T.Float(0.2, help="seconds to animate a zoom").tag(
         sync=True
     )
 
-    pan_duration: _t.Tfloat = T.Float(0.2, help="seconds to animate a pan").tag(
+    pan_duration: "_t.Tfloat" = T.Float(0.2, help="seconds to animate a pan").tag(
         sync=True
     )
 
-    fit_duration: _t.Tfloat = T.Float(0.2, help="seconds to animate a fit").tag(
+    fit_duration: "_t.Tfloat" = T.Float(0.2, help="seconds to animate a fit").tag(
         sync=True
     )
 
-    fit_padding: _t.Tfloat = T.Float(
+    fit_padding: "_t.Tfloat" = T.Float(
         10, help="pixels of padding between visible nodes and viewport"
     ).tag(sync=True)
 
diff --git a/src/ipyforcegraph/behaviors/scales.py b/src/ipyforcegraph/behaviors/scales.py
index b4590f9..6de6bf3 100644
--- a/src/ipyforcegraph/behaviors/scales.py
+++ b/src/ipyforcegraph/behaviors/scales.py
@@ -8,15 +8,17 @@
 # Distributed under the terms of the Modified BSD License.
 
 import enum
-from typing import Any, Tuple
+from typing import TYPE_CHECKING, Any, Tuple
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from ..trait_utils import validate_enum
 from ._base import Column
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 
 class ContinuousColor(Column):
     """A column which will interpolate a numeric column on a color scale."""
@@ -63,15 +65,15 @@ class Scheme(enum.Enum):
         ylorbr = "YlOrBr"
         ylorrd = "YlOrRd"
 
-    _model_name: _t.Tstr = T.Unicode("ContinuousColorModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ContinuousColorModel").tag(sync=True)
 
-    scheme: T.Enum[str, str] = T.Enum(
+    scheme: "_t.Tenum_str_str" = T.Enum(
         values=[*[m.value for m in Scheme], *Scheme],
         help="name of a continuous ``d3-scale-chromatic`` scheme",
         allow_none=True,
     ).tag(sync=True)
 
-    domain: Tuple[float, float] = W.TypedTuple(
+    domain: "Tuple[float, float]" = W.TypedTuple(
         (0.0, 1.0),
         help=("the ``[min, max]`` to map to the scale's colors"),
     ).tag(sync=True)
@@ -98,15 +100,15 @@ class Scheme(enum.Enum):
         set3 = "Set3"
         tableau10 = "Tableau10"
 
-    _model_name: _t.Tstr = T.Unicode("OrdinalColorModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("OrdinalColorModel").tag(sync=True)
 
-    scheme: T.Enum[str, str] = T.Enum(
+    scheme: "_t.Tenum_str_str" = T.Enum(
         values=[*[m.value for m in Scheme], *Scheme],
         help="name of an ordinal ``d3-scale-chromatic`` scheme",
         allow_none=True,
     ).tag(sync=True)
 
-    domain: T.Container[Tuple[Any, ...]] = T.Tuple(
+    domain: "T.Container[Tuple[Any, ...]]" = T.Tuple(
         (0.0, 1.0),
         help=("values mapped to ordinal colors in the range"),
     ).tag(sync=True)
diff --git a/src/ipyforcegraph/behaviors/selection.py b/src/ipyforcegraph/behaviors/selection.py
index fb33263..ae9f539 100644
--- a/src/ipyforcegraph/behaviors/selection.py
+++ b/src/ipyforcegraph/behaviors/selection.py
@@ -3,21 +3,23 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Optional, Tuple, Union
+from typing import TYPE_CHECKING, Optional, Tuple, Union
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from ._base import DEFAULT_RANK, Behavior
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 
 @W.register
 class NodeSelection(Behavior):
     """Enable node selection with synced row `indices` (not ``id``) of selected
     ``nodes``."""
 
-    _model_name: _t.Tstr = T.Unicode("NodeSelectionModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("NodeSelectionModel").tag(sync=True)
 
     selected: Tuple[Union[int, str], ...] = W.TypedTuple(
         T.Union((T.Int(), T.Unicode())),
@@ -25,17 +27,17 @@ class NodeSelection(Behavior):
         help="the row indices of any selected nodes",
     ).tag(sync=True)
 
-    column_name: _t.Tstr_maybe = T.Unicode(
+    column_name: "_t.Tstr_maybe" = T.Unicode(
         None,
         help="an optional name of a ``node``'s column to update when selected",
         allow_none=True,
     ).tag(sync=True)
 
-    multiple: _t.Tbool = T.Bool(
+    multiple: "_t.Tbool" = T.Bool(
         True, help="if ``False``, only one ``node`` can be selected at a time"
     ).tag(sync=True)
 
-    selected_color: _t.Tstr = T.Unicode(
+    selected_color: "_t.Tstr" = T.Unicode(
         "rgba(179, 163, 105, 1.0)",
         help="the color of selected nodes",
     ).tag(sync=True)
@@ -49,7 +51,7 @@ def _default_rank(self) -> Optional[int]:
 class LinkSelection(Behavior):
     """Enable link selection with synced ids of selected links."""
 
-    _model_name: _t.Tstr = T.Unicode("LinkSelectionModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("LinkSelectionModel").tag(sync=True)
 
     selected: Tuple[Union[int, str], ...] = W.TypedTuple(
         T.Union((T.Int(), T.Unicode())),
@@ -57,21 +59,21 @@ class LinkSelection(Behavior):
         help="the 0-based indices of any selected links",
     ).tag(sync=True)
 
-    column_name: _t.Tstr_maybe = T.Unicode(
+    column_name: "_t.Tstr_maybe" = T.Unicode(
         None,
         help="an optional name of ``node``'s column to update when selected",
         allow_none=True,
     ).tag(sync=True)
 
-    multiple: _t.Tbool = T.Bool(
+    multiple: "_t.Tbool" = T.Bool(
         True, help="if ``False``, only one ``link`` can be selected at a time"
     ).tag(sync=True)
 
-    selected_color: _t.Tstr = T.Unicode(
+    selected_color: "_t.Tstr" = T.Unicode(
         "rgba(31, 120, 179, 1.0)", help="the color of selected links"
     ).tag(sync=True)
 
-    selected_curvature: _t.Tfloat_maybe = T.Float(
+    selected_curvature: "_t.Tfloat_maybe" = T.Float(
         None,
         allow_none=True,
         help="the curvature of selected links, default: ``None`` preserves unselected ``curvature``.",
@@ -84,7 +86,7 @@ class LinkSelection(Behavior):
         help="the line-dash of selected links, default: ``None`` preserves unselected ``line_dash``",
     ).tag(sync=True)
 
-    selected_width: _t.Tfloat = T.Float(2, help="the width of selected links").tag(
+    selected_width: "_t.Tfloat" = T.Float(2, help="the width of selected links").tag(
         sync=True
     )
 
diff --git a/src/ipyforcegraph/behaviors/shapes.py b/src/ipyforcegraph/behaviors/shapes.py
index f41e0f5..b768ad6 100644
--- a/src/ipyforcegraph/behaviors/shapes.py
+++ b/src/ipyforcegraph/behaviors/shapes.py
@@ -3,12 +3,11 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Any, Optional, Sequence, Tuple, Union
+from typing import TYPE_CHECKING, Any, Optional, Sequence, Tuple, Union
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from ..trait_utils import JSON_TYPES, coerce
 from ._base import (
     DEFAULT_RANK,
@@ -22,6 +21,9 @@
     _make_trait,
 )
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 
 @W.register
 class Text(HasFillAndStroke, HasOffsets):
@@ -30,7 +32,7 @@ class Text(HasFillAndStroke, HasOffsets):
     If the ``text`` trait is (or evaluates to) ``0`` or ``None``, no shape will be drawn.
     """
 
-    _model_name: _t.Tstr = T.Unicode("TextShapeModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("TextShapeModel").tag(sync=True)
 
     text: TFeature = _make_trait("the text of a shape")
     font: TFeature = _make_trait("the font face of a shape")
@@ -62,7 +64,7 @@ class Ellipse(HasDimensions):
     If the ``width`` trait is (or evaluates to) ``0`` or ``None``, no shape will be drawn.
     """
 
-    _model_name: _t.Tstr = T.Unicode("EllipseShapeModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("EllipseShapeModel").tag(sync=True)
 
 
 @W.register
@@ -72,7 +74,7 @@ class Rectangle(HasDimensions):
     If the ``width`` trait is (or evaluates to) ``0`` or ``None``, no shape will be drawn.
     """
 
-    _model_name: _t.Tstr = T.Unicode("RectangleShapeModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("RectangleShapeModel").tag(sync=True)
 
 
 @W.register
@@ -87,7 +89,7 @@ class NodeShapes(Behavior):
     user selection.
     """
 
-    _model_name: _t.Tstr = T.Unicode("NodeShapeModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("NodeShapeModel").tag(sync=True)
 
     size: TFeature = _make_trait("the size of the default circle shape", numeric=True)
     color: TFeature = _make_trait("the color of the default circle shape")
@@ -123,7 +125,7 @@ class LinkShapes(Behavior):
         ``line_dash`` is not displayed in :class:`~ipyforcegraph.graphs.ForceGraph3D`.
     """
 
-    _model_name: _t.Tstr = T.Unicode("LinkShapeModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("LinkShapeModel").tag(sync=True)
 
     color: TFeature = _make_trait("the color of the link")
     curvature: TNumFeature = _make_trait(
@@ -164,7 +166,7 @@ def _validate_link_shape_arrays(self, proposal: T.Bunch) -> Any:
 class LinkArrows(Behavior):
     """Customize the size, position, and color of arrows on ``links``."""
 
-    _model_name: _t.Tstr = T.Unicode("LinkArrowModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("LinkArrowModel").tag(sync=True)
 
     color: TFeature = _make_trait("the color of the arrow")
     length: TNumFeature = _make_trait("the length of the arrow", numeric=True)
diff --git a/src/ipyforcegraph/behaviors/tooltip.py b/src/ipyforcegraph/behaviors/tooltip.py
index 0e0fac2..91b6803 100644
--- a/src/ipyforcegraph/behaviors/tooltip.py
+++ b/src/ipyforcegraph/behaviors/tooltip.py
@@ -3,14 +3,16 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Any, Optional
+from typing import TYPE_CHECKING, Any, Optional
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from ._base import Behavior, TFeature, _make_trait
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 
 @W.register
 class NodeTooltip(Behavior):
@@ -19,7 +21,7 @@ class NodeTooltip(Behavior):
     These may be strings or full HTML.
     """
 
-    _model_name: _t.Tstr = T.Unicode("NodeTooltipModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("NodeTooltipModel").tag(sync=True)
 
     label: TFeature = _make_trait(
         "the label to display when hovering over the ``node``, can be ``Column`` or ``Nunjucks`` template",
@@ -38,7 +40,7 @@ class LinkTooltip(Behavior):
     These may be strings or full HTML.
     """
 
-    _model_name: _t.Tstr = T.Unicode("LinkTooltipModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("LinkTooltipModel").tag(sync=True)
 
     label: TFeature = _make_trait(
         "the label to display when hovering over the ``link``, can be ``Column`` or ``Nunjucks`` template",
diff --git a/src/ipyforcegraph/behaviors/wrappers.py b/src/ipyforcegraph/behaviors/wrappers.py
index a7a4987..da028ca 100644
--- a/src/ipyforcegraph/behaviors/wrappers.py
+++ b/src/ipyforcegraph/behaviors/wrappers.py
@@ -4,12 +4,11 @@
 # Distributed under the terms of the Modified BSD License.
 
 import enum
-from typing import Any, Union
+from typing import TYPE_CHECKING, Any, Union
 
 import ipywidgets as W
 import traitlets as T
 
-from .. import _types as _t
 from .._base import ForceBase
 from ..constants import RESERVED_COLUMNS
 from ..trait_utils import validate_enum
@@ -18,6 +17,10 @@
 TAnyWrapped = Union[DynamicValue, "WrapperBase", str, bool, int, float]
 
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
+
 def _make_color_channel(name: str) -> Any:
     """Create a color channel"""
     return T.Float(
@@ -28,9 +31,9 @@ def _make_color_channel(name: str) -> Any:
 class WrapperBase(ForceBase):
     """A wrapper for other dynamic values"""
 
-    _model_name: _t.Tstr = T.Unicode("WrapperBaseModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("WrapperBaseModel").tag(sync=True)
 
-    wrapped: T.TraitType[TAnyWrapped, TAnyWrapped] = T.Union(
+    wrapped: "T.TraitType[TAnyWrapped, TAnyWrapped]" = T.Union(
         [
             T.Instance(DynamicValue),
             T.Instance("ipyforcegraph.behaviors.wrappers.WrapperBase"),
@@ -77,9 +80,9 @@ def __repr__(self) -> str:
 class CaptureAs(WrapperBase):
     """A wrapper that stores dynamically-computed values in the underlying ``node`` or ``link`."""
 
-    _model_name: _t.Tstr = T.Unicode("CaptureAsModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("CaptureAsModel").tag(sync=True)
 
-    column_name: _t.Tstr = T.Unicode(
+    column_name: "_t.Tstr" = T.Unicode(
         allow_none=False, help="name of a column to update with a derived value"
     ).tag(sync=True)
 
@@ -98,7 +101,7 @@ def _validate_column_name(self, proposal: T.Bunch) -> str:
 class ReplaceCssVariables(WrapperBase):
     """A wrapper that replaces all CSS ``var(--)`` values in the wrapped value."""
 
-    _model_name: _t.Tstr = T.Unicode("ReplaceCssVariablesModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ReplaceCssVariablesModel").tag(sync=True)
 
 
 class Colorize(WrapperBase):
@@ -115,22 +118,22 @@ class Space(enum.Enum):
         hcl = "hcl"
         cubehelix = "cubehelix"
 
-    _model_name: _t.Tstr = T.Unicode("ColorizeModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ColorizeModel").tag(sync=True)
 
-    space: T.Enum[str, str] = T.Enum(
+    space: "_t.Tenum_str_str" = T.Enum(
         default_value=Space.hsl.value,
         values=[*[m.value for m in Space], *Space],
         help="name of a ``d3-color`` color space",
     ).tag(sync=True)
 
-    a: _t.Tfloat_maybe = _make_color_channel("a*")
-    b: _t.Tfloat_maybe = _make_color_channel("blue (or ``b*``)")
-    c: _t.Tfloat_maybe = _make_color_channel("chroma")
-    g: _t.Tfloat_maybe = _make_color_channel("green")
-    h: _t.Tfloat_maybe = _make_color_channel("hue")
-    l: _t.Tfloat_maybe = _make_color_channel("luminance (or lightness)")  # noqa: E741
-    r: _t.Tfloat_maybe = _make_color_channel("red")
-    s: _t.Tfloat_maybe = _make_color_channel("saturation")
+    a: "_t.Tfloat_maybe" = _make_color_channel("a*")
+    b: "_t.Tfloat_maybe" = _make_color_channel("blue (or ``b*``)")
+    c: "_t.Tfloat_maybe" = _make_color_channel("chroma")
+    g: "_t.Tfloat_maybe" = _make_color_channel("green")
+    h: "_t.Tfloat_maybe" = _make_color_channel("hue")
+    l: "_t.Tfloat_maybe" = _make_color_channel("luminance (or lightness)")  # noqa: E741
+    r: "_t.Tfloat_maybe" = _make_color_channel("red")
+    s: "_t.Tfloat_maybe" = _make_color_channel("saturation")
     opacity: float = _make_color_channel("opacity")
 
     @T.validate("space")
@@ -141,6 +144,6 @@ def _validate_enum(self, proposal: T.Bunch) -> Any:
 class Tint(WrapperBase):
     """Apply a uniform lighten/darken amount to a color."""
 
-    _model_name: _t.Tstr = T.Unicode("TintModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("TintModel").tag(sync=True)
 
     value: float = _make_color_channel("tint")
diff --git a/src/ipyforcegraph/graphs.py b/src/ipyforcegraph/graphs.py
index 1f4b22a..8780a9b 100644
--- a/src/ipyforcegraph/graphs.py
+++ b/src/ipyforcegraph/graphs.py
@@ -3,30 +3,32 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Any, Tuple
+from typing import TYPE_CHECKING, Any, Tuple
 
 import ipywidgets as W
 import traitlets as T
 
-from . import _types as _t
 from ._base import ForceBase
 from .behaviors import Behavior
 from .behaviors._base import _make_trait
 from .sources.dataframe import DataFrameSource
 
+if TYPE_CHECKING:
+    from . import _types as _t
+
 
 @W.register
 class ForceGraph(W.DOMWidget, ForceBase):
     """Base force-directed graph widget."""
 
-    _model_name: _t.Tstr = T.Unicode("ForceGraphModel").tag(sync=True)
-    _view_name: _t.Tstr = T.Unicode("ForceGraphView").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ForceGraphModel").tag(sync=True)
+    _view_name: "_t.Tstr" = T.Unicode("ForceGraphView").tag(sync=True)
 
-    source: T.Instance[DataFrameSource] = T.Instance(
+    source: "T.Instance[DataFrameSource]" = T.Instance(
         DataFrameSource, kw={}, help="the source of ``node`` and ``link`` data"
     ).tag(sync=True, **W.widget_serialization)
 
-    behaviors: Tuple[Behavior, ...] = W.TypedTuple(
+    behaviors: "Tuple[Behavior, ...]" = W.TypedTuple(
         T.Instance(Behavior),
         kw={},
         help=(
@@ -40,22 +42,22 @@ class ForceGraph(W.DOMWidget, ForceBase):
         ),
     ).tag(sync=True, **W.widget_serialization)
 
-    default_node_color: _t.Tstr = T.Unicode(
+    default_node_color: "_t.Tstr" = T.Unicode(
         "rgba(31, 120, 179, 1.0)",
         help="a default ``node`` color, which can be overridden by :class:`~ipyforcegraph.behaviors.shapes.NodeShapes`",
     ).tag(sync=True)
 
-    default_node_size: _t.Tfloat = T.Float(
+    default_node_size: "_t.Tfloat" = T.Float(
         1,
         help="a default ``node`` size, which can be overridden by :class:`~ipyforcegraph.behaviors.shapes.NodeShapes`",
     ).tag(sync=True)
 
-    default_link_color: _t.Tstr = T.Unicode(
+    default_link_color: "_t.Tstr" = T.Unicode(
         "rgba(66, 66, 66, 0.5)",
         help="a default ``link`` color, which can be overridden by :class:`~ipyforcegraph.behaviors.shapes.LinkShapes`",
     ).tag(sync=True)
 
-    default_link_width: _t.Tfloat = T.Float(
+    default_link_width: "_t.Tfloat" = T.Float(
         1.0,
         help="a default ``link`` width, which can be overridden by :class:`~ipyforcegraph.behaviors.shapes.LinkShapes`",
     ).tag(sync=True)
@@ -77,5 +79,5 @@ def reheat(self) -> None:
 class ForceGraph3D(ForceGraph):
     """3D force-directed graph widget."""
 
-    _model_name: _t.Tstr = T.Unicode("ForceGraph3DModel").tag(sync=True)
-    _view_name: _t.Tstr = T.Unicode("ForceGraph3DView").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("ForceGraph3DModel").tag(sync=True)
+    _view_name: "_t.Tstr" = T.Unicode("ForceGraph3DView").tag(sync=True)
diff --git a/src/ipyforcegraph/sources/dataframe.py b/src/ipyforcegraph/sources/dataframe.py
index 2a6c5af..2720097 100644
--- a/src/ipyforcegraph/sources/dataframe.py
+++ b/src/ipyforcegraph/sources/dataframe.py
@@ -1,7 +1,7 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Tuple
+from typing import TYPE_CHECKING, Tuple
 
 import ipywidgets as W
 import numpy as N
@@ -9,22 +9,24 @@
 import traitlets as T
 import traittypes as TT
 
-from .. import _types as _t
 from .._base import ForceBase
 from ..serializers import dataframe_serialization
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 
 @W.register
 class DataFrameSource(ForceBase):
     """A Graph Source that stores the ``nodes`` and ``links`` as :class:`~pandas.DataFrame` instances."""
 
-    _model_name: _t.Tstr = T.Unicode("DataFrameSourceModel").tag(sync=True)
+    _model_name: "_t.Tstr" = T.Unicode("DataFrameSourceModel").tag(sync=True)
 
     nodes: P.DataFrame = TT.PandasType(
         klass=P.DataFrame, help="the :class:`~pandas.DataFrame` of node data"
     ).tag(sync=True, **dataframe_serialization)
 
-    node_id_column: _t.Tstr = T.Unicode(
+    node_id_column: "_t.Tstr" = T.Unicode(
         "id",
         help="the name of the column for a node's identifier, or 0-based position in the column if `None`",
     ).tag(sync=True)
@@ -33,7 +35,7 @@ class DataFrameSource(ForceBase):
         T.Unicode(), help="columns to preserve when updating ``nodes``"
     ).tag(sync=True)
 
-    link_id_column: _t.Tstr = T.Unicode(
+    link_id_column: "_t.Tstr" = T.Unicode(
         "id",
         help="the name of the column for a links's identifier, or 0-based position in the column if `None`",
     ).tag(sync=True)
@@ -46,12 +48,12 @@ class DataFrameSource(ForceBase):
         klass=P.DataFrame, help="the :class:`~pandas.DataFrame` of link data"
     ).tag(sync=True, **dataframe_serialization)
 
-    link_source_column: _t.Tstr = T.Unicode(
+    link_source_column: "_t.Tstr" = T.Unicode(
         "source",
         help="the name of the column for a link's source, defaulting to ``source``",
     ).tag(sync=True)
 
-    link_target_column: _t.Tstr = T.Unicode(
+    link_target_column: "_t.Tstr" = T.Unicode(
         "target",
         help="the name of the column for a link's target, defaulting to ``target``",
     ).tag(sync=True)
diff --git a/src/ipyforcegraph/sources/dodo.py b/src/ipyforcegraph/sources/dodo.py
index 6080e46..a37762e 100644
--- a/src/ipyforcegraph/sources/dodo.py
+++ b/src/ipyforcegraph/sources/dodo.py
@@ -12,7 +12,7 @@
 from copy import deepcopy
 from importlib.util import module_from_spec, spec_from_file_location
 from pathlib import Path
-from typing import Any, Dict, List, Union
+from typing import TYPE_CHECKING, Any, Dict, List, Union
 from uuid import uuid4
 
 import pandas as P
@@ -22,44 +22,47 @@
 from doit.dependency import Dependency, JsonDB, SqliteDB
 from doit.task import Task
 
-from .. import _types as _t
 from .dataframe import DataFrameSource
 
 TAnyDict = Dict[str, Any]
 Tasks = List[Task]
 
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
+
 class DodoSource(DataFrameSource):
     """A source that displays the files, tasks, and dependencies of a ``dodo.py``."""
 
-    graph_data: _t.Tdict_any = T.Dict(
+    graph_data: "_t.Tdict_any" = T.Dict(
         help="an internal collection of observed Data"
     ).tag(sync=False)
 
-    project_root: T.TraitType[Path, Union[str, Path]] = T.Union(
+    project_root: "T.TraitType[Path, Union[str, Path]]" = T.Union(
         [T.Unicode(), T.Instance(Path)],
         help="a path to a folder that contains a ``dodo.py``",
     ).tag(sync=False)
 
-    backend: _t.Tstr = T.Unicode(
+    backend: "_t.Tstr" = T.Unicode(
         "sqlite3", help="the backend for ``doit``'s dependency state"
     ).tag(sync=False)
 
-    dep_file: _t.Tstr = T.Unicode(
+    dep_file: "_t.Tstr" = T.Unicode(
         ".doit.db",
         help="the path to ``doit``'s ``dep_file``, relative to the ``project_root``",
     ).tag(sync=False)
 
-    dodo_file: _t.Tstr = T.Unicode(
+    dodo_file: "_t.Tstr" = T.Unicode(
         "dodo.py",
         help="the path to a ``dodo.py``, relative to the ``project_root``",
     ).tag(sync=True)
 
-    show_files: _t.Tbool = T.Bool(
+    show_files: "_t.Tbool" = T.Bool(
         True, help="create a node for each file, or collapse to dep groups"
     ).tag(sync=False)
 
-    show_directories: _t.Tbool = T.Bool(
+    show_directories: "_t.Tbool" = T.Bool(
         False, help="create nodes for directories, and links for containment"
     ).tag(sync=False)
 
diff --git a/src/ipyforcegraph/sources/widget.py b/src/ipyforcegraph/sources/widget.py
index 7f0e2ef..e2f6dfa 100644
--- a/src/ipyforcegraph/sources/widget.py
+++ b/src/ipyforcegraph/sources/widget.py
@@ -1,16 +1,18 @@
 # Copyright (c) 2023 ipyforcegraph contributors.
 # Distributed under the terms of the Modified BSD License.
 
-from typing import Any, Dict, Optional, Tuple, Type
+from typing import TYPE_CHECKING, Any, Dict, Optional, Tuple, Type
 
 import IPython
 import ipywidgets as W
 import pandas as P
 import traitlets as T
 
-from .. import _types as _t
 from .dataframe import DataFrameSource
 
+if TYPE_CHECKING:
+    from .. import _types as _t
+
 TAnyDict = Dict[str, Any]
 
 
@@ -26,7 +28,7 @@ class WidgetSource(DataFrameSource):
         T.Instance(T.HasTraits), help="the traitleted from which to discover data"
     )
 
-    graph_data: _t.Tdict_any = T.Dict(
+    graph_data: "_t.Tdict_any" = T.Dict(
         help="an internal collection of observed Data"
     ).tag(sync=False)