diff --git a/CHANGELOG.md b/CHANGELOG.md
index 66dd1094b..bc397efd9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,7 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - #277: The method `Pattern.print_pattern` is now deprecated.
-- Moved all device interface functionalities to an external library and removed their implementation from this library.
+- #261: Moved all device interface functionalities to an external library and removed their implementation from this library.
 
 ## [0.3.1] - 2025-04-21
 
diff --git a/graphix/command.py b/graphix/command.py
index 97c6d656a..a2fc52b1d 100644
--- a/graphix/command.py
+++ b/graphix/command.py
@@ -18,7 +18,7 @@
 # Ruff suggests to move this import to a type-checking block, but dataclass requires it here
 from graphix.parameter import ExpressionOrFloat  # noqa: TC001
 from graphix.pauli import Pauli
-from graphix.pretty_print import DataclassPrettyPrintMixin
+from graphix.repr_mixins import DataclassReprMixin
 from graphix.states import BasicStates, State
 
 Node = int
@@ -46,7 +46,7 @@ def __init_subclass__(cls) -> None:
 
 
 @dataclasses.dataclass(repr=False)
-class N(_KindChecker, DataclassPrettyPrintMixin):
+class N(_KindChecker, DataclassReprMixin):
     r"""Preparation command.
 
     Parameters
@@ -63,7 +63,7 @@ class N(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclasses.dataclass(repr=False)
-class M(_KindChecker, DataclassPrettyPrintMixin):
+class M(_KindChecker, DataclassReprMixin):
     r"""Measurement command.
 
     Parameters
@@ -112,7 +112,7 @@ def clifford(self, clifford_gate: Clifford) -> M:
 
 
 @dataclasses.dataclass(repr=False)
-class E(_KindChecker, DataclassPrettyPrintMixin):
+class E(_KindChecker, DataclassReprMixin):
     r"""Entanglement command between two qubits.
 
     Parameters
@@ -126,7 +126,7 @@ class E(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclasses.dataclass(repr=False)
-class C(_KindChecker, DataclassPrettyPrintMixin):
+class C(_KindChecker, DataclassReprMixin):
     r"""Local Clifford gate command.
 
     Parameters
@@ -143,7 +143,7 @@ class C(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclasses.dataclass(repr=False)
-class X(_KindChecker, DataclassPrettyPrintMixin):
+class X(_KindChecker, DataclassReprMixin):
     r"""X correction command.
 
     Parameters
@@ -160,7 +160,7 @@ class X(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclasses.dataclass(repr=False)
-class Z(_KindChecker, DataclassPrettyPrintMixin):
+class Z(_KindChecker, DataclassReprMixin):
     r"""Z correction command.
 
     Parameters
@@ -177,7 +177,7 @@ class Z(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclasses.dataclass(repr=False)
-class S(_KindChecker, DataclassPrettyPrintMixin):
+class S(_KindChecker, DataclassReprMixin):
     r"""S command.
 
     Parameters
diff --git a/graphix/fundamentals.py b/graphix/fundamentals.py
index 8967c7174..3f5de0103 100644
--- a/graphix/fundamentals.py
+++ b/graphix/fundamentals.py
@@ -12,7 +12,7 @@
 
 from graphix.ops import Ops
 from graphix.parameter import cos_sin
-from graphix.pretty_print import EnumPrettyPrintMixin
+from graphix.repr_mixins import EnumReprMixin
 
 if TYPE_CHECKING:
     import numpy as np
@@ -29,7 +29,7 @@
     SupportsComplexCtor = Union[SupportsComplex, SupportsFloat, SupportsIndex, complex]
 
 
-class Sign(EnumPrettyPrintMixin, Enum):
+class Sign(EnumReprMixin, Enum):
     """Sign, plus or minus."""
 
     PLUS = 1
@@ -112,7 +112,7 @@ def __complex__(self) -> complex:
         return complex(self.value)
 
 
-class ComplexUnit(EnumPrettyPrintMixin, Enum):
+class ComplexUnit(EnumReprMixin, Enum):
     """
     Complex unit: 1, -1, j, -j.
 
@@ -214,7 +214,7 @@ def matrix(self) -> npt.NDArray[np.complex128]:
         typing_extensions.assert_never(self)
 
 
-class Axis(EnumPrettyPrintMixin, Enum):
+class Axis(EnumReprMixin, Enum):
     """Axis: *X*, *Y* or *Z*."""
 
     X = enum.auto()
@@ -233,7 +233,7 @@ def matrix(self) -> npt.NDArray[np.complex128]:
         typing_extensions.assert_never(self)
 
 
-class Plane(EnumPrettyPrintMixin, Enum):
+class Plane(EnumReprMixin, Enum):
     # TODO: Refactor using match
     """Plane: *XY*, *YZ* or *XZ*."""
 
diff --git a/graphix/instruction.py b/graphix/instruction.py
index b5dfc6256..382cfa257 100644
--- a/graphix/instruction.py
+++ b/graphix/instruction.py
@@ -14,7 +14,8 @@
 
 # Ruff suggests to move this import to a type-checking block, but dataclass requires it here
 from graphix.parameter import ExpressionOrFloat  # noqa: TC001
-from graphix.pretty_print import DataclassPrettyPrintMixin, OutputFormat, angle_to_str
+from graphix.pretty_print import OutputFormat, angle_to_str
+from graphix.repr_mixins import DataclassReprMixin
 
 
 def repr_angle(angle: ExpressionOrFloat) -> str:
@@ -65,7 +66,7 @@ def __init_subclass__(cls) -> None:
 
 
 @dataclass(repr=False)
-class CCX(_KindChecker, DataclassPrettyPrintMixin):
+class CCX(_KindChecker, DataclassReprMixin):
     """Toffoli circuit instruction."""
 
     target: int
@@ -74,7 +75,7 @@ class CCX(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class RZZ(_KindChecker, DataclassPrettyPrintMixin):
+class RZZ(_KindChecker, DataclassReprMixin):
     """RZZ circuit instruction."""
 
     target: int
@@ -87,7 +88,7 @@ class RZZ(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class CNOT(_KindChecker, DataclassPrettyPrintMixin):
+class CNOT(_KindChecker, DataclassReprMixin):
     """CNOT circuit instruction."""
 
     target: int
@@ -96,7 +97,7 @@ class CNOT(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class SWAP(_KindChecker, DataclassPrettyPrintMixin):
+class SWAP(_KindChecker, DataclassReprMixin):
     """SWAP circuit instruction."""
 
     targets: tuple[int, int]
@@ -104,7 +105,7 @@ class SWAP(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class H(_KindChecker, DataclassPrettyPrintMixin):
+class H(_KindChecker, DataclassReprMixin):
     """H circuit instruction."""
 
     target: int
@@ -112,7 +113,7 @@ class H(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class S(_KindChecker, DataclassPrettyPrintMixin):
+class S(_KindChecker, DataclassReprMixin):
     """S circuit instruction."""
 
     target: int
@@ -120,7 +121,7 @@ class S(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class X(_KindChecker, DataclassPrettyPrintMixin):
+class X(_KindChecker, DataclassReprMixin):
     """X circuit instruction."""
 
     target: int
@@ -128,7 +129,7 @@ class X(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class Y(_KindChecker, DataclassPrettyPrintMixin):
+class Y(_KindChecker, DataclassReprMixin):
     """Y circuit instruction."""
 
     target: int
@@ -136,7 +137,7 @@ class Y(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class Z(_KindChecker, DataclassPrettyPrintMixin):
+class Z(_KindChecker, DataclassReprMixin):
     """Z circuit instruction."""
 
     target: int
@@ -144,7 +145,7 @@ class Z(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class I(_KindChecker, DataclassPrettyPrintMixin):
+class I(_KindChecker, DataclassReprMixin):
     """I circuit instruction."""
 
     target: int
@@ -152,7 +153,7 @@ class I(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class M(_KindChecker, DataclassPrettyPrintMixin):
+class M(_KindChecker, DataclassReprMixin):
     """M circuit instruction."""
 
     target: int
@@ -162,7 +163,7 @@ class M(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class RX(_KindChecker, DataclassPrettyPrintMixin):
+class RX(_KindChecker, DataclassReprMixin):
     """X rotation circuit instruction."""
 
     target: int
@@ -172,7 +173,7 @@ class RX(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class RY(_KindChecker, DataclassPrettyPrintMixin):
+class RY(_KindChecker, DataclassReprMixin):
     """Y rotation circuit instruction."""
 
     target: int
@@ -182,7 +183,7 @@ class RY(_KindChecker, DataclassPrettyPrintMixin):
 
 
 @dataclass(repr=False)
-class RZ(_KindChecker, DataclassPrettyPrintMixin):
+class RZ(_KindChecker, DataclassReprMixin):
     """Z rotation circuit instruction."""
 
     target: int
diff --git a/graphix/pretty_print.py b/graphix/pretty_print.py
index b28fe6038..2892ce174 100644
--- a/graphix/pretty_print.py
+++ b/graphix/pretty_print.py
@@ -2,23 +2,19 @@
 
 from __future__ import annotations
 
-import dataclasses
 import enum
 import math
 import string
-from dataclasses import MISSING
 from enum import Enum
 from fractions import Fraction
 from typing import TYPE_CHECKING, SupportsFloat
 
 from graphix import command
+from graphix.fundamentals import Plane
 
 if TYPE_CHECKING:
     from collections.abc import Container
 
-    # these live only in the stub package, not at runtime
-    from _typeshed import DataclassInstance
-
     from graphix.command import Node
     from graphix.pattern import Pattern
 
@@ -106,9 +102,6 @@ def command_to_str(cmd: command.Command, output: OutputFormat) -> str:
     output: OutputFormat
         The expected format.
     """
-    # Circumvent circular import
-    from graphix.fundamentals import Plane
-
     out = [cmd.kind.name]
 
     if cmd.kind == command.CommandKind.E:
@@ -223,64 +216,3 @@ def pattern_to_str(
     if truncated:
         return f"{result}...({len(command_list) - limit + 1} more commands)"
     return result
-
-
-class DataclassPrettyPrintMixin:
-    """
-    Mixin for a concise, eval-friendly `repr` of dataclasses.
-
-    Compared to the default dataclass `repr`:
-      - Class variables are omitted (dataclasses.fields only returns actual fields).
-      - Fields whose values equal their defaults are omitted.
-      - Field names are only shown when preceding fields have been omitted, ensuring positional listings when possible.
-
-    Use with `@dataclass(repr=False)` on the target class.
-    """
-
-    def __repr__(self: DataclassInstance) -> str:
-        """Return a representation string for a dataclass."""
-        cls_name = type(self).__name__
-        arguments = []
-        saw_omitted = False
-        for field in dataclasses.fields(self):
-            value = getattr(self, field.name)
-            if field.default is not MISSING or field.default_factory is not MISSING:
-                default = field.default_factory() if field.default_factory is not MISSING else field.default
-                if value == default:
-                    saw_omitted = True
-                    continue
-            custom_repr = field.metadata.get("repr")
-            value_str = custom_repr(value) if custom_repr else repr(value)
-            if saw_omitted:
-                arguments.append(f"{field.name}={value_str}")
-            else:
-                arguments.append(value_str)
-        arguments_str = ", ".join(arguments)
-        return f"{cls_name}({arguments_str})"
-
-
-class EnumPrettyPrintMixin:
-    """
-    Mixin to provide a concise, eval-friendly repr for Enum members.
-
-    Compared to the default `<ClassName.MEMBER_NAME: value>`, this mixin's `__repr__`
-    returns `ClassName.MEMBER_NAME`, which can be evaluated in Python (assuming the
-    enum class is in scope) to retrieve the same member.
-    """
-
-    def __repr__(self) -> str:
-        """
-        Return a representation string of an Enum member.
-
-        Returns
-        -------
-        str
-            A string in the form `ClassName.MEMBER_NAME`.
-        """
-        # Equivalently (as of Python 3.12), `str(value)` also produces
-        # "ClassName.MEMBER_NAME", but we build it explicitly here for
-        # clarity.
-        if not isinstance(self, Enum):
-            msg = "EnumMixin can only be used with Enum classes."
-            raise TypeError(msg)
-        return f"{self.__class__.__name__}.{self.name}"
diff --git a/graphix/pyzx.py b/graphix/pyzx.py
index 138282581..e3d355483 100644
--- a/graphix/pyzx.py
+++ b/graphix/pyzx.py
@@ -45,12 +45,6 @@ def to_pyzx_graph(og: OpenGraph) -> BaseGraph[int, tuple[int, int]]:
     >>> og = OpenGraph(g, measurements, inputs, outputs)
     >>> reconstructed_pyzx_graph = to_pyzx_graph(og)
     """
-    # check pyzx availability and version
-    try:
-        import pyzx as zx
-    except ModuleNotFoundError as e:
-        msg = "Cannot find pyzx (optional dependency)."
-        raise RuntimeError(msg) from e
     if zx.__version__ != "0.9.0":
         warnings.warn(
             "`to_pyzx_graph` is guaranteed to work only with pyzx==0.9.0 due to possible breaking changes in `pyzx`.",
diff --git a/graphix/random_objects.py b/graphix/random_objects.py
index f4c8f50c6..d47e96f2e 100644
--- a/graphix/random_objects.py
+++ b/graphix/random_objects.py
@@ -13,6 +13,7 @@
 from graphix.channels import KrausChannel, KrausData
 from graphix.ops import Ops
 from graphix.rng import ensure_rng
+from graphix.sim.density_matrix import DensityMatrix
 from graphix.transpiler import Circuit
 
 if TYPE_CHECKING:
@@ -21,7 +22,6 @@
     from numpy.random import Generator
 
     from graphix.parameter import Parameter
-    from graphix.sim.density_matrix import DensityMatrix
 
 
 def rand_herm(sz: int, rng: Generator | None = None) -> npt.NDArray:
@@ -80,8 +80,6 @@ def rand_dm(
     dm = rand_u @ dm @ rand_u.transpose().conj()
 
     if dm_dtype:
-        from graphix.sim.density_matrix import DensityMatrix  # circumvent circular import
-
         # will raise an error if incorrect dimension
         return DensityMatrix(data=dm)
     return dm
diff --git a/graphix/repr_mixins.py b/graphix/repr_mixins.py
new file mode 100644
index 000000000..70907e904
--- /dev/null
+++ b/graphix/repr_mixins.py
@@ -0,0 +1,73 @@
+"""Mixins for eval-friendly `repr` for dataclasses and Enum members."""
+
+from __future__ import annotations
+
+import dataclasses
+from dataclasses import MISSING
+from enum import Enum
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    # these live only in the stub package, not at runtime
+    from _typeshed import DataclassInstance
+
+
+class DataclassReprMixin:
+    """
+    Mixin for a concise, eval-friendly `repr` of dataclasses.
+
+    Compared to the default dataclass `repr`:
+      - Class variables are omitted (dataclasses.fields only returns actual fields).
+      - Fields whose values equal their defaults are omitted.
+      - Field names are only shown when preceding fields have been omitted, ensuring positional listings when possible.
+
+    Use with `@dataclass(repr=False)` on the target class.
+    """
+
+    def __repr__(self: DataclassInstance) -> str:
+        """Return a representation string for a dataclass."""
+        cls_name = type(self).__name__
+        arguments = []
+        saw_omitted = False
+        for field in dataclasses.fields(self):
+            value = getattr(self, field.name)
+            if field.default is not MISSING or field.default_factory is not MISSING:
+                default = field.default_factory() if field.default_factory is not MISSING else field.default
+                if value == default:
+                    saw_omitted = True
+                    continue
+            custom_repr = field.metadata.get("repr")
+            value_str = custom_repr(value) if custom_repr else repr(value)
+            if saw_omitted:
+                arguments.append(f"{field.name}={value_str}")
+            else:
+                arguments.append(value_str)
+        arguments_str = ", ".join(arguments)
+        return f"{cls_name}({arguments_str})"
+
+
+class EnumReprMixin:
+    """
+    Mixin to provide a concise, eval-friendly repr for Enum members.
+
+    Compared to the default `<ClassName.MEMBER_NAME: value>`, this mixin's `__repr__`
+    returns `ClassName.MEMBER_NAME`, which can be evaluated in Python (assuming the
+    enum class is in scope) to retrieve the same member.
+    """
+
+    def __repr__(self) -> str:
+        """
+        Return a representation string of an Enum member.
+
+        Returns
+        -------
+        str
+            A string in the form `ClassName.MEMBER_NAME`.
+        """
+        # Equivalently (as of Python 3.12), `str(value)` also produces
+        # "ClassName.MEMBER_NAME", but we build it explicitly here for
+        # clarity.
+        if not isinstance(self, Enum):
+            msg = "EnumMixin can only be used with Enum classes."
+            raise TypeError(msg)
+        return f"{self.__class__.__name__}.{self.name}"
diff --git a/graphix/utils.py b/graphix/utils.py
index e6817b17b..326ce421b 100644
--- a/graphix/utils.py
+++ b/graphix/utils.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import inspect
 import sys
 import typing
 from typing import TYPE_CHECKING, Any, ClassVar, Literal, SupportsInt, TypeVar
@@ -31,8 +32,6 @@ def check_kind(cls: type, scope: dict[str, Any]) -> None:
         # MEMO: `inspect.get_annotations` unavailable
         return
 
-    import inspect
-
     ann = inspect.get_annotations(cls, eval_str=True, locals=scope).get("kind")
     if ann is None:
         msg = "kind must be annotated."
diff --git a/pyproject.toml b/pyproject.toml
index 1716822e9..a0832f015 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -67,7 +67,6 @@ extend-ignore = [
   "DOC",     # Docstring
   "E501",    # Line too long
   "EM10",    # Raise string
-  "PLC0415", # Import not at the top level
   "PLR1702", # Too many nests
   "PLW1641", # __hash__ missing
   "PT011",   # pytest raises too broad
diff --git a/tests/test_pyzx.py b/tests/test_pyzx.py
index ea3ca6275..cd0d0486d 100644
--- a/tests/test_pyzx.py
+++ b/tests/test_pyzx.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import importlib.util  # Use fully-qualified import to avoid name conflict (util)
 import random
 from copy import deepcopy
 from typing import TYPE_CHECKING
@@ -13,22 +12,29 @@
 from graphix.random_objects import rand_circuit
 from graphix.transpiler import Circuit
 
-if TYPE_CHECKING:
-    from pyzx.graph.base import BaseGraph
+try:
+    import pyzx as zx
+    from pyzx.generate import cliffordT as clifford_t  # noqa: N813
 
-SEED = 123
+    from graphix.pyzx import from_pyzx_graph, to_pyzx_graph
+except ImportError:
+    pytestmark = pytest.mark.skip(reason="pyzx not installed")
 
+    if TYPE_CHECKING:
+        import sys
 
-def _pyzx_notfound() -> bool:
-    return importlib.util.find_spec("pyzx") is None
+        # We skip type-checking the case where there is no pyzx, since
+        # pyright cannot figure out that tests are skipped in this
+        # case.
+        sys.exit(1)
 
 
-@pytest.mark.skipif(_pyzx_notfound(), reason="pyzx not installed")
-def test_graph_equality() -> None:
-    from pyzx.generate import cliffordT as clifford_t  # noqa: N813
+if TYPE_CHECKING:
+    from pyzx.graph.base import BaseGraph
+SEED = 123
 
-    from graphix.pyzx import from_pyzx_graph
 
+def test_graph_equality() -> None:
     random.seed(SEED)
     g = clifford_t(4, 10, 0.1)
 
@@ -42,10 +48,6 @@ def test_graph_equality() -> None:
 
 def assert_reconstructed_pyzx_graph_equal(g: BaseGraph[int, tuple[int, int]]) -> None:
     """Convert a graph to and from an Open graph and then checks the resulting pyzx graph is equal to the original."""
-    import pyzx as zx
-
-    from graphix.pyzx import from_pyzx_graph, to_pyzx_graph
-
     zx.simplify.to_graph_like(g)
 
     g_copy = deepcopy(g)
@@ -66,20 +68,14 @@ def assert_reconstructed_pyzx_graph_equal(g: BaseGraph[int, tuple[int, int]]) ->
 # Tests that compiling from a pyzx graph to an OpenGraph returns the same
 # graph. Only works with small circuits up to 4 qubits since PyZX's `tensorfy`
 # function seems to consume huge amount of memory for larger qubit
-@pytest.mark.skipif(_pyzx_notfound(), reason="pyzx not installed")
 def test_random_clifford_t() -> None:
-    from pyzx.generate import cliffordT as clifford_t  # noqa: N813
-
     for _ in range(15):
         g = clifford_t(4, 10, 0.1)
         assert_reconstructed_pyzx_graph_equal(g)
 
 
-@pytest.mark.skipif(_pyzx_notfound(), reason="pyzx not installed")
 @pytest.mark.parametrize("jumps", range(1, 11))
 def test_random_circuit(fx_bg: PCG64, jumps: int) -> None:
-    from graphix.pyzx import from_pyzx_graph, to_pyzx_graph
-
     rng = Generator(fx_bg.jumped(jumps))
     nqubits = 5
     depth = 5
@@ -98,12 +94,7 @@ def test_random_circuit(fx_bg: PCG64, jumps: int) -> None:
     assert np.abs(np.dot(state.flatten().conjugate(), state2.flatten())) == pytest.approx(1)
 
 
-@pytest.mark.skipif(_pyzx_notfound(), reason="pyzx not installed")
 def test_rz() -> None:
-    import pyzx as zx
-
-    from graphix.pyzx import from_pyzx_graph
-
     circuit = Circuit(2)
     circuit.rz(0, np.pi / 4)
     pattern = circuit.transpile().pattern
@@ -117,12 +108,7 @@ def test_rz() -> None:
 
 
 # Issue #235
-@pytest.mark.skipif(_pyzx_notfound(), reason="pyzx not installed")
 def test_full_reduce_toffoli() -> None:
-    import pyzx as zx
-
-    from graphix.pyzx import from_pyzx_graph, to_pyzx_graph
-
     c = Circuit(3)
     c.ccx(0, 1, 2)
     p = c.transpile().pattern