Defer imports on the cold import path

changelog.d/1547.change.md

@@ -0,0 +1 @@
+The import time for `import attr` and `import attrs` has been _significantly_ improved by making expensive imports lazy.

src/attr/__init__.py

@@ -4,10 +4,12 @@
 Classes Without Boilerplate
 """
 
+import sys
+
 from functools import partial
 from typing import Callable, Literal, Protocol
 
-from . import converters, exceptions, filters, setters, validators
+from . import exceptions, filters, setters
 from ._cmp import cmp_using
 from ._config import get_run_validators, set_run_validators
 from ._funcs import asdict, assoc, astuple, has, resolve_types
@@ -78,13 +80,23 @@ class AttrsInstance(Protocol):
 ]
 
 
+_LAZY_SUBMODULES = {"converters", "validators"}
+
+
 def _make_getattr(mod_name: str) -> Callable:
     """
     Create a metadata proxy for packaging information that uses *mod_name* in
     its warnings and errors.
     """
 
     def __getattr__(name: str) -> str:
+        if name in _LAZY_SUBMODULES:
+            import importlib
+
+            mod = importlib.import_module(f".{name}", mod_name)
+            sys.modules[mod_name].__dict__[name] = mod
+            return mod
+
         if name not in ("__version__", "__version_info__"):
             msg = f"module {mod_name} has no attribute {name}"
             raise AttributeError(msg)
@@ -102,3 +114,7 @@ def __getattr__(name: str) -> str:
 
 
 __getattr__ = _make_getattr(__name__)
+
+
+def __dir__() -> list[str]:
+    return sorted(set(globals()) | set(__all__))

src/attr/_compat.py

@@ -1,15 +1,13 @@
 # SPDX-License-Identifier: MIT
 
-import inspect
-import platform
 import sys
 import threading
 
 from collections.abc import Mapping, Sequence  # noqa: F401
 from typing import _GenericAlias
 
 
-PYPY = platform.python_implementation() == "PyPy"
+PYPY = sys.implementation.name == "pypy"
 PY_3_10_PLUS = sys.version_info[:2] >= (3, 10)
 PY_3_11_PLUS = sys.version_info[:2] >= (3, 11)
 PY_3_12_PLUS = sys.version_info[:2] >= (3, 12)
@@ -18,12 +16,12 @@
 
 
 if PY_3_14_PLUS:
-    import annotationlib
-
     # We request forward-ref annotations to not break in the presence of
     # forward references.
 
     def _get_annotations(cls):
+        import annotationlib
+
         return annotationlib.get_annotations(
             cls, format=annotationlib.Format.FORWARDREF
         )
@@ -46,6 +44,8 @@ class _AnnotationExtractor:
     __slots__ = ["sig"]
 
     def __init__(self, callable):
+        import inspect
+
         try:
             self.sig = inspect.signature(callable)
         except (ValueError, TypeError):  # inspect failed
@@ -55,6 +55,8 @@ def get_first_param_type(self):
         """
         Return the type annotation of the first argument if it's not empty.
         """
+        import inspect
+
         if not self.sig:
             return None
 
@@ -68,6 +70,8 @@ def get_return_type(self):
         """
         Return the return type if it's not empty.
         """
+        import inspect
+
         if (
             self.sig
             and self.sig.return_annotation is not inspect.Signature.empty

src/attr/_funcs.py

@@ -1,8 +1,6 @@
 # SPDX-License-Identifier: MIT
 
 
-import copy
-
 from ._compat import get_generic_base
 from ._make import _OBJ_SETATTR, NOTHING, fields
 from .exceptions import AttrsAttributeNotFoundError
@@ -411,6 +409,8 @@ def assoc(inst, **changes):
         removed du to the slightly different approach compared to
         `attrs.evolve`, though.
     """
+    import copy
+
     new = copy.copy(inst)
     attrs = fields(inst.__class__)
     for k, v in changes.items():

src/attr/_make.py

@@ -4,9 +4,7 @@
 
 import abc
 import contextlib
-import copy
 import enum
-import inspect
 import itertools
 import linecache
 import sys
@@ -705,6 +703,8 @@ def __init__(
         if self._has_pre_init:
             # Check if the pre init method has more arguments than just `self`
             # We want to pass arguments if pre init expects arguments
+            import inspect
+
             pre_init_func = cls.__attrs_pre_init__
             pre_init_signature = inspect.signature(pre_init_func)
             self._pre_init_has_args = len(pre_init_signature.parameters) > 1
@@ -920,6 +920,8 @@ def _create_slots_class(self):
         # To know to update them.
         additional_closure_functions_to_update = []
         if cached_properties:
+            import inspect
+
             class_annotations = _get_annotations(self._cls)
             for name, func in cached_properties.items():
                 # Add cached properties to names for slotting.
@@ -2613,6 +2615,8 @@ def evolve(self, **changes):
 
         .. versionadded:: 20.3.0
         """
+        import copy
+
         new = copy.copy(self)
 
         new._setattrs(changes.items())

src/attrs/__init__.py

@@ -25,7 +25,7 @@
 from attr._make import ClassProps
 from attr._next_gen import asdict, astuple, inspect
 
-from . import converters, exceptions, filters, setters, validators
+from . import exceptions, filters, setters
 
 
 __all__ = [
@@ -70,3 +70,7 @@
 ]
 
 __getattr__ = _make_getattr(__name__)
+
+
+def __dir__() -> list[str]:
+    return sorted(set(globals()) | set(__all__))

tests/test_import.py

@@ -1,5 +1,8 @@
 # SPDX-License-Identifier: MIT
 
+import attr
+import attrs
+
 
 class TestImportStar:
     def test_from_attr_import_star(self):
@@ -9,3 +12,23 @@ def test_from_attr_import_star(self):
         # attr_import_star contains `from attr import *`, which cannot
         # be done here because *-imports are only allowed on module level.
         from . import attr_import_star  # noqa: F401
+
+
+class TestDir:
+    def test_attr_dir_includes_lazy_submodules(self):
+        """
+        converters and validators are listed in dir(attr).
+        """
+        assert "converters" in dir(attr)
+        assert "validators" in dir(attr)
+        assert "__name__" in dir(attr)
+        assert "_make_getattr" in dir(attr)
+
+    def test_attrs_dir_includes_lazy_submodules(self):
+        """
+        converters and validators are listed in dir(attrs).
+        """
+        assert "converters" in dir(attrs)
+        assert "validators" in dir(attrs)
+        assert "__name__" in dir(attrs)
+        assert "_make_getattr" in dir(attrs)