Fix get_nexrad_location mutating shared NEXRAD_LOCATIONS table

pyart/io/nexrad_common.py

@@ -26,10 +26,17 @@ def get_nexrad_location(station):
     """
     loc = NEXRAD_LOCATIONS[station.upper()]
 
-    # Convert from feet to meters for elevation units
-    loc["elev"] = loc["elev"] * 0.3048
+    # Convert from feet to meters for elevation units. Read into a local
+    # variable and return a new value rather than writing back into
+    # loc["elev"] -- loc is a reference into the shared, module-level
+    # NEXRAD_LOCATIONS dict, so mutating it in place applied this
+    # conversion permanently. A second call for the same station then
+    # converted the already-converted value again, silently corrupting
+    # the elevation (e.g. KTLX: 1213 ft -> 369.72 m on the first call,
+    # then -> 112.7 m on the second).
+    elev_m = loc["elev"] * 0.3048
 
-    return loc["lat"], loc["lon"], loc["elev"]
+    return loc["lat"], loc["lon"], elev_m
 
 
 # Locations of NEXRAD locations was retrieved from NOAA's

tests/io/test_nexrad_common.py

@@ -0,0 +1,29 @@
+"""Unit Tests for Py-ART's io/nexrad_common.py module."""
+
+import pytest
+
+from pyart.io import nexrad_common
+
+
+def test_get_nexrad_location_known_station():
+    lat, lon, elev = nexrad_common.get_nexrad_location("KTLX")
+    assert lat == pytest.approx(35.33306, abs=1e-3)
+    assert lon == pytest.approx(-97.2775, abs=1e-3)
+    # bundled table stores elevation in feet (1213 ft); function must
+    # return meters
+    assert elev == pytest.approx(1213 * 0.3048, abs=1e-6)
+
+
+def test_get_nexrad_location_repeated_calls_are_stable():
+    # Regression test: get_nexrad_location used to mutate the shared
+    # NEXRAD_LOCATIONS dict in place (loc["elev"] = loc["elev"] * 0.3048,
+    # where loc is a reference into the module-level table, not a copy).
+    # A second call for the same station then applied the feet->meters
+    # conversion again on top of the already-converted value, silently
+    # corrupting the elevation.
+    _, _, elev_first = nexrad_common.get_nexrad_location("KTLX")
+    _, _, elev_second = nexrad_common.get_nexrad_location("KTLX")
+    _, _, elev_third = nexrad_common.get_nexrad_location("KTLX")
+    assert elev_first == elev_second == elev_third
+    # and the underlying table itself must be untouched (still in feet)
+    assert nexrad_common.NEXRAD_LOCATIONS["KTLX"]["elev"] == 1213