✨ Support typing.Literal in Python 3.8+

docs/tutorial/parameter-types/enum.md

@@ -153,3 +153,51 @@ Buying groceries: Eggs, Bacon
 ```
 
 </div>
+
+
+### Literal choices
+
+With Python 3.8+, you can also use `typing.Literal` to represent a set of possible predefined choices, without having to use an `Enum`:
+
+=== "Python 3.7+"
+
+    ```Python hl_lines="6"
+    {!> ../docs_src/parameter_types/enum/tutorial004_an.py!}
+    ```
+
+=== "Python 3.7+ non-Annotated"
+
+    !!! tip
+        Prefer to use the `Annotated` version if possible.
+
+    ```Python hl_lines="5"
+    {!> ../docs_src/parameter_types/enum/tutorial004.py!}
+    ```
+
+<div class="termy">
+
+```console
+$ python main.py --help
+
+// Notice the predefined values [simple|conv|lstm]
+Usage: main.py [OPTIONS]
+
+Options:
+  --network [simple|conv|lstm]  [default: simple]
+  --help                        Show this message and exit.
+
+// Try it
+$ python main.py --network conv
+
+Training neural network of type: conv
+
+// Invalid value
+$ python main.py --network capsule
+
+Usage: main.py [OPTIONS]
+Try "main.py --help" for help.
+
+Error: Invalid value for '--network': 'capsule' is not one of 'simple', 'conv', 'lstm'.
+```
+
+</div>

docs_src/parameter_types/enum/tutorial004.py

@@ -0,0 +1,10 @@
+import typer
+from typing_extensions import Literal
+
+
+def main(network: Literal["simple", "conv", "lstm"] = typer.Option("simple")):
+    print(f"Training neural network of type: {network}")
+
+
+if __name__ == "__main__":
+    typer.run(main)

docs_src/parameter_types/enum/tutorial004_an.py

@@ -0,0 +1,12 @@
+import typer
+from typing_extensions import Annotated, Literal
+
+
+def main(
+    network: Annotated[Literal["simple", "conv", "lstm"], typer.Option()] = "simple",
+):
+    print(f"Training neural network of type: {network}")
+
+
+if __name__ == "__main__":
+    typer.run(main)

tests/test_tutorial/test_parameter_types/test_enum/test_tutorial004.py

@@ -0,0 +1,52 @@
+import subprocess
+import sys
+
+import typer
+from typer.testing import CliRunner
+
+from docs_src.parameter_types.enum import tutorial004 as mod
+
+from ....utils import needs_py38
+
+runner = CliRunner()
+
+app = typer.Typer()
+app.command()(mod.main)
+
+
+@needs_py38
+def test_help():
+    result = runner.invoke(app, ["--help"])
+    assert result.exit_code == 0
+    assert "--network [simple|conv|lstm]" in result.output.replace("  ", "")
+
+
+@needs_py38
+def test_main():
+    result = runner.invoke(app, ["--network", "conv"])
+    assert result.exit_code == 0
+    assert "Training neural network of type: conv" in result.output
+
+
+@needs_py38
+def test_invalid():
+    result = runner.invoke(app, ["--network", "capsule"])
+    assert result.exit_code != 0
+    assert (
+        "Invalid value for '--network': invalid choice: capsule. (choose from"
+        in result.output
+        or "Invalid value for '--network': 'capsule' is not one of" in result.output
+    )
+    assert "simple" in result.output
+    assert "conv" in result.output
+    assert "lstm" in result.output
+
+
+@needs_py38
+def test_script():
+    result = subprocess.run(
+        [sys.executable, "-m", "coverage", "run", mod.__file__, "--help"],
+        capture_output=True,
+        encoding="utf-8",
+    )
+    assert "Usage" in result.stdout

tests/test_tutorial/test_parameter_types/test_enum/test_tutorial004_an.py

@@ -0,0 +1,52 @@
+import subprocess
+import sys
+
+import typer
+from typer.testing import CliRunner
+
+from docs_src.parameter_types.enum import tutorial004_an as mod
+
+from ....utils import needs_py38
+
+runner = CliRunner()
+
+app = typer.Typer()
+app.command()(mod.main)
+
+
+@needs_py38
+def test_help():
+    result = runner.invoke(app, ["--help"])
+    assert result.exit_code == 0
+    assert "--network [simple|conv|lstm]" in result.output.replace("  ", "")
+
+
+@needs_py38
+def test_main():
+    result = runner.invoke(app, ["--network", "conv"])
+    assert result.exit_code == 0
+    assert "Training neural network of type: conv" in result.output
+
+
+@needs_py38
+def test_invalid():
+    result = runner.invoke(app, ["--network", "capsule"])
+    assert result.exit_code != 0
+    assert (
+        "Invalid value for '--network': invalid choice: capsule. (choose from"
+        in result.output
+        or "Invalid value for '--network': 'capsule' is not one of" in result.output
+    )
+    assert "simple" in result.output
+    assert "conv" in result.output
+    assert "lstm" in result.output
+
+
+@needs_py38
+def test_script():
+    result = subprocess.run(
+        [sys.executable, "-m", "coverage", "run", mod.__file__, "--help"],
+        capture_output=True,
+        encoding="utf-8",
+    )
+    assert "Usage" in result.stdout

tests/utils.py

@@ -13,6 +13,7 @@
 except ShellDetectionFailure:  # pragma: no cover
     shell = None
 
+needs_py38 = pytest.mark.skipif(sys.version_info < (3, 8), reason="requires python3.8+")
 
 needs_py310 = pytest.mark.skipif(
     sys.version_info < (3, 10), reason="requires python3.10+"

typer/main.py

@@ -14,7 +14,7 @@
 import click
 from typing_extensions import get_args, get_origin
 
-from ._typing import is_union
+from ._typing import is_literal_type, is_union, literal_values
 from .completion import get_completion_inspect_parameters
 from .core import (
     DEFAULT_MARKUP_MODE,
@@ -797,6 +797,11 @@ def get_click_type(
             [item.value for item in annotation],
             case_sensitive=parameter_info.case_sensitive,
         )
+    elif is_literal_type(annotation):
+        return click.Choice(
+            literal_values(annotation),
+            case_sensitive=parameter_info.case_sensitive,
+        )
     raise RuntimeError(f"Type not yet supported: {annotation}")  # pragma: no cover