FIX: Fix incorrect error message on start()

Author: nmacholl

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## 0.16.1 - TBD
+
+#### Bug fixes
+- Fixed an issue where starting a `Live` client before subscribing gave an incorrect error message
+
 ## 0.16.0 - 2023-07-25
 
 This release includes updates to the fields in text encodings (CSV and JSON), you can read more about the changes [here](https://databento.com/blog/CSV-JSON-updates-july-2023).

databento/live/client.py

@@ -357,6 +357,7 @@ def start(
         ValueError
             If `start()` is called before a subscription has been made.
             If `start()` is called after streaming has already started.
+            If `start()` is called after the live session has closed.
 
         See Also
         --------
@@ -365,6 +366,8 @@ def start(
         """
         logger.info("starting live client")
         if not self.is_connected():
+            if self.dataset == "":
+                raise ValueError("cannot start a live client without a subscription")
             raise ValueError("cannot start a live client after it is closed")
         if self._session.is_started():
             raise ValueError("client is already started")

databento/version.py

@@ -1 +1 @@
-__version__ = "0.16.0"
+__version__ = "0.16.1"

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "databento"
-version = "0.16.0"
+version = "0.16.1"
 description = "Official Python client library for Databento"
 authors = [
     "Databento <[email protected]>",

tests/test_live_client.py

@@ -309,6 +309,14 @@ def test_live_start_twice(
     with pytest.raises(ValueError):
         live_client.start()
 
+def test_live_start_before_subscribe(
+    live_client: client.Live,
+) -> None:
+    """
+    Test that calling start() before subscribe raises a ValueError.
+    """
+    with pytest.raises(ValueError):
+        live_client.start()
 
 @pytest.mark.parametrize(
     "schema",