Defer heavy imports to speed up import time

tests/test_traitlets.py

@@ -1657,6 +1657,11 @@ def coerce(self, value):
         return pathlib.Path(value)
 
 
+def test_path_from_string():
+    assert Path().from_string("foo/bar") == pathlib.Path("foo/bar")
+    assert Path(allow_none=True).from_string("None") is None
+
+
 class ListTrait(HasTraits):
     value = List(Int())
 
@@ -3040,6 +3045,15 @@ def test_list_from_string(s, expected):
     _from_string_test(List, s, expected)
 
 
+def test_container_from_string_list_deprecated_literal():
+    # Passing a whole container literal as a single --opt="[...]" element is
+    # deprecated (traitlets 5.0) but still supported.
+    trait = List(Integer())
+    trait.name = "x"
+    with pytest.warns(DeprecationWarning, match="is deprecated in traitlets 5.0"):
+        assert trait.from_string_list(["[1, 2, 3]"]) == [1, 2, 3]
+
+
 @pytest.mark.parametrize(
     "s, expected, value_trait",
     [

traitlets/config/application.py

@@ -5,17 +5,14 @@
 from __future__ import annotations
 
 import functools
-import json
 import logging
 import os
-import pprint
 import re
 import sys
 import typing as t
 from collections import OrderedDict, defaultdict
 from contextlib import suppress
 from copy import deepcopy
-from logging.config import dictConfig
 from textwrap import dedent
 
 from traitlets.config.configurable import Configurable, SingletonConfigurable
@@ -286,6 +283,8 @@ def _observe_logging_default(self, change: Bunch) -> None:
         self._configure_logging()
 
     def _configure_logging(self) -> None:
+        from logging.config import dictConfig
+
         config = self.get_default_logging_config()
         nested_update(config, self.logging_config or {})
         dictConfig(config)
@@ -483,6 +482,8 @@ def start_show_config(self) -> None:
                 cls_config.pop("show_config_json", None)
 
         if self.show_config_json:
+            import json
+
             json.dump(config, sys.stdout, indent=1, sort_keys=True, default=repr)
             # add trailing newline
             sys.stdout.write("\n")
@@ -498,6 +499,8 @@ def start_show_config(self) -> None:
             class_config = config[classname]
             if not class_config:
                 continue
+            import pprint
+
             print(classname)
             pformat_kwargs: StrDict = dict(indent=4, compact=True)  # noqa: C408
 
@@ -929,6 +932,8 @@ def _load_config_files(
                     if log:
                         log.debug("Loaded config file: %s", loader.full_filename)
                 if config:
+                    import json
+
                     for filename, earlier_config in zip(filenames, loaded, strict=True):
                         collisions = earlier_config.collisions(config)
                         if collisions and log:

traitlets/config/loader.py

@@ -7,7 +7,6 @@
 import argparse
 import copy
 import functools
-import json
 import os
 import re
 import sys
@@ -577,6 +576,8 @@ def load_config(self) -> Config:
         return self.config
 
     def _read_file_as_dict(self) -> dict[str, t.Any]:
+        import json
+
         with open(self.full_filename) as f:
             return t.cast("dict[str, t.Any]", json.load(f))
 
@@ -603,6 +604,8 @@ def __exit__(self, exc_type: object, exc_value: object, traceback: object) -> No
         configuration to disk.
         """
         self.config.version = 1
+        import json
+
         json_config = json.dumps(self.config, indent=2)
         with open(self.full_filename, "w") as f:
             f.write(json_config)

traitlets/traitlets.py

@@ -43,15 +43,12 @@
 
 import contextlib
 import enum
-import inspect
 import numbers
 import os
-import pathlib
 import re
 import sys
 import types
 import typing as t
-from ast import literal_eval
 
 from .utils.bunch import Bunch
 from .utils.descriptions import add_article, class_of, describe, repr_type
@@ -63,6 +60,8 @@
 SequenceTypes = (list, tuple, set, frozenset)
 
 if t.TYPE_CHECKING:
+    import pathlib
+
     from typing_extensions import TypeVar
 else:
     from typing import TypeVar
@@ -185,6 +184,8 @@ def _safe_literal_eval(s: str) -> t.Any:
 
     Use only where types are ambiguous.
     """
+    from ast import literal_eval
+
     try:
         return literal_eval(s)
     except (NameError, SyntaxError, ValueError):
@@ -559,7 +560,7 @@ def __init__(
 
         if len(kwargs) > 0:
             stacklevel = 1
-            f = inspect.currentframe()
+            f: types.FrameType | None = sys._getframe()
             # count supers to determine stacklevel for warning
             assert f is not None
             while f.f_code.co_name == "__init__":
@@ -974,7 +975,7 @@ def __new__(
             # ----------------------------------------------------------------
             # Support of deprecated behavior allowing for TraitType types
             # to be used instead of TraitType instances.
-            if inspect.isclass(v) and issubclass(v, TraitType):
+            if isinstance(v, type) and issubclass(v, TraitType):
                 warn(
                     "Traits should be given as instances, not types (for example, `Int()`, not `Int`)."
                     " Passing types is deprecated in traitlets 4.1.",
@@ -2114,7 +2115,7 @@ def __init__(
             else:
                 klass = default_value
 
-        if not (inspect.isclass(klass) or isinstance(klass, str)):
+        if not isinstance(klass, (type, str)):
             raise TraitError("A Type trait must specify a class.")
 
         self.klass = klass
@@ -2278,7 +2279,7 @@ class or its subclasses.  Our implementation is quite different
         if klass is None:
             klass = self.klass
 
-        if (klass is not None) and (inspect.isclass(klass) or isinstance(klass, str)):
+        if (klass is not None) and isinstance(klass, (type, str)):
             self.klass = klass
         else:
             raise TraitError(f"The klass attribute must be a class not: {klass!r}")
@@ -3510,6 +3511,8 @@ def from_string(self, s: str) -> T | None:
         """Load value from a single string"""
         if not isinstance(s, str):
             raise TraitError(f"Expected string, got {s!r}")
+        from ast import literal_eval
+
         try:
             test = literal_eval(s)
         except Exception:
@@ -3542,7 +3545,11 @@ def from_string_list(self, s_list: list[str]) -> T | None:
                     DeprecationWarning,
                     stacklevel=2,
                 )
+                from ast import literal_eval
+
                 return self.klass(literal_eval(r))  # type:ignore[call-arg]
+        import inspect
+
         sig = inspect.signature(self.item_from_string)
         if "index" in sig.parameters:
             item_from_string = self.item_from_string
@@ -4069,6 +4076,7 @@ def from_string_list(self, s_list: list[str]) -> t.Any:
                 DeprecationWarning,
                 stacklevel=2,
             )
+            from ast import literal_eval
 
             return literal_eval(s_list[0])
 
@@ -4192,11 +4200,15 @@ class Path(TraitType["pathlib.Path", t.Union["pathlib.Path", str, "os.PathLike[s
     info_text = "a filesystem path"
 
     def validate(self, obj: t.Any, value: t.Any) -> pathlib.Path | None:
+        import pathlib
+
         if isinstance(value, (str, os.PathLike)):
             return pathlib.Path(value)
         self.error(obj, value)
 
     def from_string(self, s: str) -> pathlib.Path | None:
+        import pathlib
+
         if self.allow_none and s == "None":
             return None
         return pathlib.Path(s)

traitlets/utils/__init__.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import os
-import pathlib
 from collections.abc import Sequence
 
 
@@ -51,6 +50,8 @@ def filefind(filename: str, path_dirs: Sequence[str] | None = None) -> str:
     if os.path.isabs(filename) and os.path.isfile(filename):
         return filename
 
+    import pathlib
+
     if path_dirs is None:
         path_dirs = ("",)
     elif isinstance(path_dirs, str):

traitlets/utils/decorators.py

@@ -3,14 +3,15 @@
 from __future__ import annotations
 
 import copy
-from inspect import Parameter, Signature, signature
 from typing import Any, TypeVar
 
 from ..traitlets import HasTraits, Undefined
 
 
 def _get_default(value: Any) -> Any:
     """Get default argument value, given the trait default value."""
+    from inspect import Parameter
+
     return Parameter.empty if value == Undefined else value
 
 
@@ -19,6 +20,8 @@ def _get_default(value: Any) -> Any:
 
 def signature_has_traits(cls: type[T]) -> type[T]:
     """Return a decorated class with a constructor signature that contain Trait names as kwargs."""
+    from inspect import Parameter, Signature, signature
+
     traits = [
         (name, _get_default(value.default_value))
         for name, value in cls.class_traits().items()

traitlets/utils/descriptions.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import inspect
 import re
 import types
 from typing import Any
@@ -71,14 +70,14 @@ class name where an object was defined.
     if isinstance(article, str):
         article = article.lower()
 
-    if not inspect.isclass(value):
+    if not isinstance(value, type):
         typename = type(value).__name__
     else:
         typename = value.__name__
     if verbose:
         typename = _prefix(value) + typename
 
-    if article == "the" or (article is None and not inspect.isclass(value)):
+    if article == "the" or (article is None and not isinstance(value, type)):
         if name is not None:
             result = f"{typename} {name}"
             if article is not None:
@@ -87,7 +86,7 @@ class name where an object was defined.
                 return result
         else:
             tick_wrap = False
-            if inspect.isclass(value):
+            if isinstance(value, type):
                 name = value.__name__
             elif isinstance(value, types.FunctionType):
                 name = value.__name__
@@ -123,6 +122,8 @@ def _prefix(value: Any) -> str:
     if isinstance(value, types.MethodType):
         name = describe(None, value.__self__, verbose=True) + "."
     else:
+        import inspect
+
         module = inspect.getmodule(value)
         if module is not None and module.__name__ != "builtins":
             name = module.__name__ + "."
@@ -136,7 +137,7 @@ def class_of(value: Any) -> Any:
 
     For example 'an Image' or 'a PlotValue'.
     """
-    if inspect.isclass(value):
+    if isinstance(value, type):
         return add_article(value.__name__)
     else:
         return class_of(type(value))

traitlets/utils/getargspec.py

@@ -10,15 +10,19 @@
 
 from __future__ import annotations
 
-import inspect
-from functools import partial
-from typing import Any
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    import inspect
 
 # Unmodified from sphinx below this line
 
 
 def getargspec(func: Any) -> inspect.FullArgSpec:
     """Like inspect.getargspec but supports functools.partial as well."""
+    import inspect
+    from functools import partial
+
     if inspect.ismethod(func):
         func = func.__func__
     if type(func) is partial:

traitlets/utils/warnings.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import inspect
 import os
 import typing as t
 import warnings
@@ -20,6 +19,8 @@ def deprecated_method(method: t.Any, cls: t.Any, method_name: str, msg: str) ->
     Uses warn_explicit to bind warning to method definition instead of triggering code,
     which isn't relevant.
     """
+    import inspect
+
     warn_msg = f"{cls.__name__}.{method_name} is deprecated in traitlets 4.1: {msg}"
 
     for parent in inspect.getmro(cls):