Don't eagerly load the Locale, nor pytest until it's needed.

The main problem here was that importing pendulum.testing.traveller was
importing time_machine, which was also importing pytest.

And creating the DifferenceFormatter at import time was also loading the
locale.

Both of these are "optional" in the sense that there is lots you can do in
Pendulum without ever using them, so we can relatively straightforwardly delay
things until they are requested.

Tested by running `uv run --with time_machine -p 3.12 python -Ximporttime -c 'import pendulum'`:

- Before: ~50-64ms (a lot of noise)
- After: 20-29ms

Not a huge slow down, but I figured it was worth it anyway, especially not not
load pytest.

Author: ashb

src/pendulum/__init__.py

@@ -2,6 +2,8 @@
 
 import datetime as _datetime
 
+from functools import cache
+from typing import TYPE_CHECKING
 from typing import Any
 from typing import Union
 from typing import cast
@@ -30,7 +32,6 @@
 from pendulum.helpers import week_starts_at
 from pendulum.interval import Interval
 from pendulum.parser import parse as parse
-from pendulum.testing.traveller import Traveller
 from pendulum.time import Time
 from pendulum.tz import UTC
 from pendulum.tz import fixed_timezone
@@ -334,17 +335,43 @@ def interval(
     return Interval(start, end, absolute=absolute)
 
 
-# Testing
+if TYPE_CHECKING:
+    from pendulum.testing.traveller import Traveller
 
-_traveller = Traveller(DateTime)
+    _traveller = Traveller(DateTime)
+    freeze = _traveller.freeze
+    travel = _traveller.travel
+    travel_to = _traveller.travel_to
+    travel_back = _traveller.travel_back
+else:
+    # We do this in an if-not-typing block so we don't have to duplicate the function signatures.
+    @cache
+    def _traveller() -> Traveller:
+        # Lazy load this, so we don't eagerly load Pytest if we don't need to
+        from pendulum.testing.traveller import Traveller
 
-freeze = _traveller.freeze
-travel = _traveller.travel
-travel_to = _traveller.travel_to
-travel_back = _traveller.travel_back
+        return Traveller(DateTime)
+
+    def freeze(*args, **kwargs) -> Traveller:
+        return _traveller().freeze(*args, **kwargs)
+
+    def travel(*args, **kwargs):
+        _traveller().travel(*args, **kwargs)
+
+    def travel_to(*args, **kwargs):
+        _traveller().travel_to(*args, **kwargs)
+
+    def travel_back(*args, **kwargs):
+        _traveller().travel_back(*args, **kwargs)
 
 
 def __getattr__(name: str) -> Any:
+    if name == "Traveller":
+        # This wasn't in `__all__`, but it was defined before, so keep it for back compat
+        from pendulum.testing.traveller import Traveller
+
+        return Traveller
+
     if name == "__version__":
         import importlib.metadata
         import warnings

src/pendulum/helpers.py

@@ -6,23 +6,27 @@
 from datetime import date
 from datetime import datetime
 from datetime import timedelta
+from functools import cache
 from math import copysign
 from typing import TYPE_CHECKING
+from typing import Any
 from typing import TypeVar
 from typing import overload
 
 import pendulum
 
 from pendulum.constants import DAYS_PER_MONTHS
 from pendulum.day import WeekDay
-from pendulum.formatting.difference_formatter import DifferenceFormatter
 from pendulum.locales.locale import Locale
 
 
 if TYPE_CHECKING:
     # Prevent import cycles
     from pendulum.duration import Duration
 
+    # LazyLoaded
+    from pendulum.formatting.difference_formatter import DifferenceFormatter
+
 with_extensions = os.getenv("PENDULUM_EXTENSIONS", "1") == "1"
 
 _DT = TypeVar("_DT", bound=datetime)
@@ -48,7 +52,7 @@
     from pendulum._helpers import precise_diff  # type: ignore[assignment]
     from pendulum._helpers import week_day
 
-difference_formatter = DifferenceFormatter()
+difference_formatter: DifferenceFormatter
 
 
 @overload
@@ -164,7 +168,7 @@ def format_diff(
     if locale is None:
         locale = get_locale()
 
-    return difference_formatter.format(diff, is_now, absolute, locale)
+    return _difference_formatter().format(diff, is_now, absolute, locale)
 
 
 def _sign(x: float) -> int:
@@ -202,6 +206,19 @@ def week_ends_at(wday: WeekDay) -> None:
     pendulum._WEEK_ENDS_AT = wday
 
 
+@cache
+def _difference_formatter() -> DifferenceFormatter:
+    from pendulum.formatting.difference_formatter import DifferenceFormatter
+
+    return DifferenceFormatter()
+
+
+def __getattr__(name: str) -> Any:
+    if name == "difference_formatter":
+        return _difference_formatter()
+    raise AttributeError(name)
+
+
 __all__ = [
     "PreciseDiff",
     "add_duration",

src/pendulum/locales/locale.py

@@ -2,7 +2,6 @@
 
 import re
 
-from importlib import import_module, resources
 from pathlib import Path
 from typing import Any
 from typing import ClassVar
@@ -24,6 +23,8 @@ def __init__(self, locale: str, data: Any) -> None:
 
     @classmethod
     def load(cls, locale: str | Locale) -> Locale:
+        from importlib import import_module, resources
+
         if isinstance(locale, Locale):
             return locale