Lazy-install altair and tenacity

lib/setup.py

@@ -29,7 +29,7 @@
 # - Always include the lower bound as >= VERSION, to keep testing min versions easy
 # - And include an upper bound that's < NEXT_MAJOR_VERSION
 INSTALL_REQUIRES = [
-    "altair>=4.0, <6",
+    # "altair>=4.0, <6", # HACK: For stlite, comment out as it will be lazy-installed when needed. See script_runner.py
     "blinker>=1.0.0, <2",
     "cachetools>=4.0, <6",
     # "click>=7.0, <9", # HACK: For stlite, comment out as it's not needed for stlite
@@ -49,7 +49,7 @@
     # "pyarrow>=7.0", # HACK: For stlite, comment out as it's not Pyodide-compatible
     # "requests>=2.27, <3", # HACK: For stlite, comment out as it's not Pyodide-compatible
     # "rich>=10.14.0, <14", # HACK: For stlite, comment out as rich is not really needed for stlite
-    "tenacity>=8.1.0, <9",
+    # "tenacity>=8.1.0, <9", # HACK: For stlite, comment out as it will be lazy-installed when needed. See script_runner.py
     # "toml>=0.10.1, <2", # HACK: For stlite, comment out as it's not needed for stlite
     "typing-extensions>=4.3.0, <5",
     # Don't require watchdog on MacOS, since it'll fail without xcode tools.

lib/streamlit/runtime/scriptrunner/script_runner.py

@@ -81,6 +81,17 @@ class ScriptRunnerEvent(Enum):
     ENQUEUE_FORWARD_MSG = "ENQUEUE_FORWARD_MSG"
 
 
+LAZY_INSTALL_LIST = {  # map of importable module name to PyPI package name
+    # Now only supports the packages that some of Streamlit core features depend on but excluded from its dependency list for faster installation.
+    # PIL (pillow) is not supported now. See the note in the lazy-install block in the _run_script method.
+    "altair": "altair",
+    "tenacity": "tenacity",
+}
+lazy_install_tried_modules = (
+    set()
+)  # Holds the module names we've tried to lazy-install to avoid trying again and resulting in an infinite loop.
+
+
 """
 Note [Threading]
 There are two kinds of threads in Streamlit, the main thread and script threads.
@@ -561,6 +572,37 @@ async def _run_script(self, rerun_data: RerunData) -> None:
                 premature_stop = True
 
             except Exception as ex:
+                if isinstance(ex, ImportError):
+                    # Stlite: Lazy-install
+                    # NOTE: This lazy-install mechanism doesn't catch the import errors of
+                    #       Pyodide-distributed packages such as PIL (pillow) because ModuleNotFoundError
+                    #       will be raised when trying to import instead of ImportError.
+                    #       Moreover, that ModuleNotFoundError object won't have the `name` attribute,
+                    #       so we can't get the missed module name from it in a straightforward way.
+                    #       Then, for now, we gave up supporting it as the concered package is only PIL
+                    #       and unshipping and lazy-installing it doesn't introduce so much benefit.
+                    _LOGGER.debug("ImportError: %s", ex)
+                    missed_module_name = ex.name
+                    if (
+                        missed_module_name not in lazy_install_tried_modules
+                        and missed_module_name in LAZY_INSTALL_LIST
+                    ):
+                        package_name = LAZY_INSTALL_LIST[missed_module_name]
+                        lazy_install_tried_modules.add(missed_module_name)
+                        _LOGGER.info(
+                            "Attempting to install missing module: %s", package_name
+                        )
+                        try:
+                            import micropip
+
+                            await micropip.install(package_name)
+                            continue
+                        except Exception as micropip_err:
+                            _LOGGER.warning(
+                                "Failed to lazy-install missing module: %s",
+                                micropip_err,
+                            )
+
                 self._session_state[SCRIPT_RUN_WITHOUT_ERRORS_KEY] = False
                 uncaught_exception = ex
                 handle_uncaught_app_exception(uncaught_exception)