[ENG-4647] Fix env_file handling

* Import dotenv.load_dotenv early to avoid ImportError while loading
  rxconfig.py
* Read ENV_FILE from the environment explicitly.

fix #4803

reflex/config.py

@@ -26,8 +26,12 @@
     get_origin,
 )
 
+from reflex_cli.constants.hosting import Hosting
 from typing_extensions import Annotated, get_type_hints
 
+from reflex import constants
+from reflex.base import Base
+from reflex.utils import console
 from reflex.utils.exceptions import ConfigError, EnvironmentVarValueError
 from reflex.utils.types import GenericType, is_union, value_inside_optional
 
@@ -36,11 +40,11 @@
 except ModuleNotFoundError:
     import pydantic
 
-from reflex_cli.constants.hosting import Hosting
 
-from reflex import constants
-from reflex.base import Base
-from reflex.utils import console
+try:
+    from dotenv import load_dotenv  # pyright: ignore [reportMissingImports]
+except ImportError:
+    load_dotenv = None
 
 
 class DBConfig(Base):
@@ -793,16 +797,15 @@ def update_from_env(self) -> dict[str, Any]:
         Returns:
             The updated config values.
         """
-        if self.env_file:
-            try:
-                from dotenv import load_dotenv  # pyright: ignore [reportMissingImports]
-
-                # load env file if exists
-                load_dotenv(self.env_file, override=True)
-            except ImportError:
+        env_file = self.env_file or os.environ.get("ENV_FILE", None)
+        if env_file:
+            if load_dotenv is None:
                 console.error(
                     """The `python-dotenv` package is required to load environment variables from a file. Run `pip install "python-dotenv>=1.0.1"`."""
                 )
+            else:
+                # load env file if exists
+                load_dotenv(env_file, override=True)
 
         updated_values = {}
         # Iterate over the fields.