Add get_from_env utility + tests

lib/galaxy/util/properties.py

@@ -31,6 +31,22 @@ from galaxy.util.path import (
 )
 
 
+def get_from_env(key: str, prefixes: Iterable[str], default: Optional[str] = None):
+    """
+    Return first available value for prefix+key set in the environment, or default.
+    An empty prefix is ignored.
+
+    Useful when we need to check against multiple prefixes sequentially,
+    returning the first available value.
+    """
+    for prefix in prefixes:
+        if prefix:
+            value = os.getenv(f"{prefix}{key}")
+            if value:
+                return value
+    return default
+
+
 def find_config_file(names, exts=None, dirs=None, include_samples=False):
     """Locate a config file in multiple directories, with multiple extensions.
 

test/unit/util/test_properties.py

@@ -1,8 +1,11 @@
+import os
+
 import pytest
 
 from galaxy.exceptions import InvalidFileFormatError
 from galaxy.util import properties
 from galaxy.util.properties import (
+    get_from_env,
     nice_config_parser,
     read_properties_from_file,
 )
@@ -12,6 +15,28 @@ VAL1, VAL2, VAL3, VAL4, VAL5, VAL6 = 1, 2, 3, 4, 5, 6
 OTHER_SECTION = "other"
 
 
+def test_get_from_env(monkeypatch):
+    prefixes = ["pre1_", "pre2_", "pre3_"]
+
+    monkeypatch.setenv("pre1_a", "a-is-set")
+    monkeypatch.setenv("pre2_b", "b-is-set")
+
+    assert get_from_env("a", prefixes, "a-default") == "a-is-set"  # selected from first prefix
+    assert get_from_env("b", prefixes, "b-default") == "b-is-set"  # selected from second prefix
+    assert get_from_env("c", prefixes, "c-default") == "c-default"  # default
+
+
+def test_get_from_env__no_default(monkeypatch):
+    assert get_from_env("a", ["some", "random", "prefixes"]) is None
+
+
+def test_get_from_env__empty_prefix_ignored(monkeypatch):
+    monkeypatch.setenv("a", "a-without-prefix-is-set")
+    assert os.getenv("a") == "a-without-prefix-is-set"
+
+    assert get_from_env("a", ["", None], "a-default") == "a-default"
+
+
 @pytest.fixture
 def mock_properties(monkeypatch):
     # Keys in defaults dict and other dicts should not intersect. The tests assume