Add LazyChoice class for choices where obtaining list of options is expensive (and unnecessary in some cases).

Author: domdfcoding

consolekit/options.py

@@ -79,6 +79,7 @@
 		"no_pager_option",
 		"PromptOption",
 		"ChoiceOption",
+		"LazyChoice",
 		"MultiValueOption",
 		"flag_option",
 		"auto_default_option",
@@ -590,3 +591,40 @@ def __init__(self, *args, description: Optional[str] = None, **kwargs):
 		super().__init__(*args, **kwargs)
 
 		self.description: Optional[str] = description
+
+
+# class LazyChoice(click.Choice[str]):
+class LazyChoice(click.Choice):
+	"""
+	Modified choice type that lazily loads the data.
+
+	Useful for expensive operations that need not happen if the option is not provided or the help text is not being displayed.
+
+	:param getter: Function that returns the actual choices.
+	:param case_sensitive: Set to :py:obj:`False` to make choices case insensitive.
+
+	.. versionadded:: 1.11.0
+	"""
+
+	_choices: Optional[Sequence[str]] = None
+
+	def __init__(
+			self,
+			getter: Callable[[], Iterable[str]],
+			case_sensitive: bool = True,
+			) -> None:
+		self._getter = getter
+
+		self.case_sensitive = case_sensitive
+
+	@property
+	def choices(self) -> Sequence[str]:  # type: ignore[override]
+		"""
+		The choices, obtained from the getter function and cached.
+		"""
+
+		if self._choices is None:
+			choices = tuple(self._getter())
+			self._choices = choices
+
+		return self._choices

tests/test_options.py

@@ -13,6 +13,7 @@
 from consolekit.options import (
 		ChoiceOption,
 		DescribedArgument,
+		LazyChoice,
 		MultiValueOption,
 		PromptOption,
 		auto_default_argument,
@@ -342,6 +343,41 @@ def main(station: str) -> None:
 	assert result.stdout.rstrip() == "Tuning to station: Radio 1"
 
 
+@pytest.mark.parametrize(
+		"click_version",
+		[pytest.param('7', marks=click_8_only), pytest.param('8', marks=not_click_8)],
+		)
+def test_lazy_choice(
+		advanced_file_regression: AdvancedFileRegressionFixture,
+		click_version: str,
+		cli_runner: CliRunner,
+		):
+
+	def expensive_operation():
+		print("Performing expensive operation to get choices.")
+		return ["Radio 1", "Radio 2", "Radio 3"]
+
+	@click.option(
+			"-s",
+			"--station",
+			help="The station to play.",
+			type=LazyChoice(expensive_operation, case_sensitive=False),
+			cls=ChoiceOption,
+			prompt="Select a station",
+			)
+	@click_command()
+	def main(station: str) -> None:
+		print(f"Tuning to station: {station}")
+
+	result = cli_runner.invoke(main, input="5\n0\n2\n")
+	assert result.exit_code == 0
+	advanced_file_regression.check(result.stdout.rstrip())
+
+	result = cli_runner.invoke(main, args=["--station", "Radio 1"])
+	assert result.exit_code == 0
+	assert result.stdout.rstrip() == "Tuning to station: Radio 1"
+
+
 not_click_8_or_above_82 = pytest.mark.skipif(
 		_click_major != 8 or (_click_major == 8 and _click_version[1] >= 2), reason="Output differs on click 8"
 		)

tests/test_options_/test_lazy_choice_7_.txt

@@ -0,0 +1,10 @@
+Performing expensive operation to get choices.
+ [1] Radio 1
+ [2] Radio 2
+ [3] Radio 3
+Select a station: 5
+Error: 5 is not in the valid range of 1 to 3.
+Select a station: 0
+Error: 0 is not in the valid range of 1 to 3.
+Select a station: 2
+Tuning to station: Radio 2

tests/test_options_/test_lazy_choice_8_.txt

@@ -0,0 +1,10 @@
+Performing expensive operation to get choices.
+ [1] Radio 1
+ [2] Radio 2
+ [3] Radio 3
+Select a station: 5
+Error: 5 is not in the range 1<=x<=3.
+Select a station: 0
+Error: 0 is not in the range 1<=x<=3.
+Select a station: 2
+Tuning to station: Radio 2