Add --app_args support from the CLI

examples/app_argparse/app.py

@@ -0,0 +1,28 @@
+import argparse
+
+import lightning as L
+
+
+class Work(L.LightningWork):
+    def __init__(self, cloud_compute):
+        super().__init__(cloud_compute=cloud_compute)
+
+    def run(self):
+        pass
+
+
+class Flow(L.LightningFlow):
+    def __init__(self, cloud_compute):
+        super().__init__()
+        self.work = Work(cloud_compute)
+
+    def run(self):
+        assert self.work.cloud_compute.name == "gpu", self.work.cloud_compute.name
+        self._exit()
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--use_gpu", action="store_true", default=False, help="Whether to use GPU in the cloud")
+    hparams = parser.parse_args()
+    app = L.LightningApp(Flow(L.CloudCompute("gpu" if hparams.use_gpu else "cpu")))

src/lightning_app/cli/lightning_cli.py

@@ -1,7 +1,7 @@
 import logging
 import os
 from pathlib import Path
-from typing import Tuple, Union
+from typing import List, Tuple, Union
 
 import click
 from requests.exceptions import ConnectionError
@@ -109,8 +109,17 @@ def run():
 @click.option("--blocking", "blocking", type=bool, default=False)
 @click.option("--open-ui", type=bool, default=True, help="Decide whether to launch the app UI in a web browser")
 @click.option("--env", type=str, default=[], multiple=True, help="Env variables to be set for the app.")
+@click.option("--app_args", type=str, default=[], multiple=True, help="Collection of arguments for the app.")
 def run_app(
-    file: str, cloud: bool, without_server: bool, no_cache: bool, name: str, blocking: bool, open_ui: bool, env: tuple
+    file: str,
+    cloud: bool,
+    without_server: bool,
+    no_cache: bool,
+    name: str,
+    blocking: bool,
+    open_ui: bool,
+    env: tuple,
+    app_args: List[str],
 ):
     """Run an app from a file."""
     _run_app(file, cloud, without_server, no_cache, name, blocking, open_ui, env)
@@ -263,10 +272,4 @@ def _prepare_file(file: str) -> str:
     if exists:
         return file
 
-    if not exists and file == "quick_start.py":
-        from lightning_app.demo.quick_start import app
-
-        logger.info(f"For demo purposes, Lightning will run the {app.__file__} file.")
-        return app.__file__
-
     raise FileNotFoundError(f"The provided file {file} hasn't been found.")

src/lightning_app/testing/testing.py

@@ -76,14 +76,20 @@ def restart_work(self, work_name: str):
 
 
 @requires("click")
-def application_testing(lightning_app_cls: Type[LightningTestApp], command_line: List[str] = []) -> Any:
+def application_testing(
+    lightning_app_cls: Type[LightningTestApp] = LightningTestApp, command_line: List[str] = []
+) -> Any:
     from unittest import mock
 
     from click.testing import CliRunner
 
     with mock.patch("lightning.LightningApp", lightning_app_cls):
+        original = sys.argv
+        sys.argv = command_line
         runner = CliRunner()
-        return runner.invoke(run_app, command_line, catch_exceptions=False)
+        result = runner.invoke(run_app, command_line, catch_exceptions=False)
+        sys.argv = original
+        return result
 
 
 class SingleWorkFlow(LightningFlow):

src/lightning_app/utilities/load_app.py

@@ -4,6 +4,7 @@
 import sys
 import traceback
 import types
+from contextlib import contextmanager
 from typing import Dict, List, TYPE_CHECKING, Union
 
 from lightning_app.utilities.exceptions import MisconfigurationException
@@ -26,7 +27,8 @@ def load_app_from_file(filepath: str) -> "LightningApp":
     code = _create_code(filepath)
     module = _create_fake_main_module(filepath)
     try:
-        exec(code, module.__dict__)
+        with _patch_sys_argv():
+            exec(code, module.__dict__)
     except Exception:
         # we want to format the exception as if no frame was on top.
         exp, val, tb = sys.exc_info()
@@ -113,6 +115,48 @@ def _create_fake_main_module(script_path):
     return module
 
 
+@contextmanager
+def _patch_sys_argv():
+    """This function modifies the ``sys.argv`` by extracting the arguments after ``--app_args`` and removed
+    everything else before executing the user app script.
+
+    The command: ``lightning run app app.py --without-server --app_args --use_gpu --env ...`` will be converted into
+    ``app.py --use_gpu``
+    """
+    from lightning_app.cli.lightning_cli import run_app
+
+    original_argv = sys.argv
+    # 1: Remove the CLI command
+    if sys.argv[:3] == ["lightning", "run", "app"]:
+        sys.argv = sys.argv[3:]
+
+    if "--app_args" not in sys.argv:
+        # 2: If app_args wasn't used, there is no arguments, so we assign the shorten arguments.
+        new_argv = sys.argv[:1]
+    else:
+        # 3: Collect all the arguments from the CLI
+        options = [p.opts[0] for p in run_app.params[1:] if p.opts[0] != "--app_args"]
+        argv_slice = sys.argv
+        # 4: Find the index of `app_args`
+        first_index = argv_slice.index("--app_args") + 1
+        # 5: Find the next argument from the CLI if any.
+        matches = [
+            argv_slice.index(opt) for opt in options if opt in argv_slice and argv_slice.index(opt) >= first_index
+        ]
+        if not matches:
+            last_index = len(argv_slice)
+        else:
+            last_index = min(matches)
+        # 6: last_index is either the fully command or the latest match from the CLI options.
+        new_argv = [argv_slice[0]] + argv_slice[first_index:last_index]
+
+    # 7: Patch the command
+    sys.argv = new_argv
+    yield
+    # 8: Restore the command
+    sys.argv = original_argv
+
+
 def component_to_metadata(obj: Union["LightningWork", "LightningFlow"]) -> Dict:
     from lightning_app import LightningWork
 

tests/tests_app_examples/test_argparse.py

@@ -0,0 +1,67 @@
+import os
+import sys
+
+from lightning_app import _PACKAGE_ROOT
+from lightning_app.testing.testing import application_testing
+from lightning_app.utilities.load_app import _patch_sys_argv
+
+
+def test_app_argparse_example():
+    original_argv = sys.argv
+
+    command_line = [
+        os.path.join(os.path.dirname(os.path.dirname(_PACKAGE_ROOT)), "examples/app_argparse/app.py"),
+        "--app_args",
+        "--use_gpu",
+        "--without-server",
+    ]
+    result = application_testing(command_line=command_line)
+    assert result.exit_code == 0, result.__dict__
+    assert sys.argv == original_argv
+
+
+def test_patch_sys_argv():
+    original_argv = sys.argv
+
+    sys.argv = expected = ["lightning", "run", "app", "app.py"]
+    with _patch_sys_argv():
+        assert sys.argv == ["app.py"]
+
+    assert sys.argv == expected
+
+    sys.argv = expected = ["lightning", "run", "app", "app.py", "--without-server", "--env", "name=something"]
+    with _patch_sys_argv():
+        assert sys.argv == ["app.py"]
+
+    assert sys.argv == expected
+
+    sys.argv = expected = ["lightning", "run", "app", "app.py", "--app_args"]
+    with _patch_sys_argv():
+        assert sys.argv == ["app.py"]
+
+    assert sys.argv == expected
+
+    sys.argv = expected = ["lightning", "run", "app", "app.py", "--app_args", "--env", "name=something"]
+    with _patch_sys_argv():
+        assert sys.argv == ["app.py"]
+
+    assert sys.argv == expected
+
+    sys.argv = expected = [
+        "lightning",
+        "run",
+        "app",
+        "app.py",
+        "--without-server",
+        "--app_args",
+        "--use_gpu",
+        "--name=hello",
+        "--env",
+        "name=something",
+    ]
+    with _patch_sys_argv():
+        assert sys.argv == ["app.py", "--use_gpu", "--name=hello"]
+
+    assert sys.argv == expected
+
+    sys.argv = original_argv