Moving lightning_api_access out of base requirements

requirements/app/base.txt

@@ -12,4 +12,3 @@ beautifulsoup4>=4.8.0, <4.11.2
 inquirer>=2.10.0
 psutil<5.9.4
 click<=8.1.3
-lightning_api_access>=0.0.1

requirements/app/components.txt

@@ -0,0 +1,2 @@
+# deps required by components in the lightning app repository (src/lightning_app/components)
+lightning_api_access>=0.0.1

requirements/app/devel.txt

@@ -10,4 +10,7 @@
 # extended list of dependencies for UI
 -r ./ui.txt
 
+# extended list of dependencies for UI
+-r ./components.txt
+
 -r ./examples.txt

src/lightning_app/components/serve/python_server.py

@@ -4,19 +4,24 @@
 from pathlib import Path
 from typing import Any, Dict, Optional
 
-import torch
 import uvicorn
 from fastapi import FastAPI
+from lightning_utilities.core.imports import module_available
 from pydantic import BaseModel
 from starlette.staticfiles import StaticFiles
 
 from lightning_app.core.queues import MultiProcessQueue
 from lightning_app.core.work import LightningWork
 from lightning_app.utilities.app_helpers import Logger
+from lightning_app.utilities.imports import requires
 from lightning_app.utilities.proxies import _proxy_setattr, unwrap, WorkRunExecutor, WorkStateObserver
 
 logger = Logger(__name__)
 
+# Skip doctests if requirements aren't available
+if not module_available("lightning_api_access"):
+    __doctest_skip__ = ["PythonServer", "PythonServer.*"]
+
 
 class _PyTorchSpawnRunExecutor(WorkRunExecutor):
 
@@ -86,6 +91,7 @@ def _get_sample_data() -> Dict[Any, Any]:
 
 
 class PythonServer(LightningWork, abc.ABC):
+    @requires("lightning_api_access")
     def __init__(  # type: ignore
         self,
         host: str = "127.0.0.1",
@@ -203,6 +209,8 @@ def _attach_predict_fn(self, fastapi_app: FastAPI) -> None:
         output_type: type = self.configure_output_type()
 
         def predict_fn(request: input_type):  # type: ignore
+            import torch
+
             with torch.inference_mode():
                 return self.predict(request)