[hotfix] add defaults for missing symbols

ultraplot/constructor.py

@@ -21,9 +21,11 @@
 import cycler
 import matplotlib.colors as mcolors
 import matplotlib.dates as mdates
+import matplotlib.font_manager as mfonts
 import matplotlib.projections.polar as mpolar
 import matplotlib.scale as mscale
 import matplotlib.ticker as mticker
+from matplotlib.ft2font import FT2Font
 import numpy as np
 
 from . import colors as pcolors
@@ -184,6 +186,17 @@ def _build_locator_registry() -> dict[str, object]:
     return registry
 
 
+def _get_dms_symbol_kwargs() -> dict[str, str]:
+    """Return ASCII DMS symbols when the active font lacks prime glyphs."""
+    try:
+        path = mfonts.findfont(mfonts.FontProperties())
+        font = FT2Font(path)
+        has_primes = all(font.get_char_index(ord(symbol)) for symbol in "′″")
+    except Exception:  # pragma: no cover - font lookup should be reliable
+        has_primes = False
+    return {} if has_primes else {"minute_symbol": "'", "second_symbol": '"'}
+
+
 def _build_formatter_registry() -> dict[str, object]:
     registry = {  # note default LogFormatter uses ugly e+00 notation
         "none": mticker.NullFormatter,
@@ -227,9 +240,13 @@ def _build_formatter_registry() -> dict[str, object]:
     if hasattr(mdates, "ConciseDateFormatter"):
         registry["concise"] = mdates.ConciseDateFormatter
     if _version_cartopy >= "0.18":
-        registry["dms"] = partial(pticker.DegreeFormatter, dms=True)
-        registry["dmslon"] = partial(pticker.LongitudeFormatter, dms=True)
-        registry["dmslat"] = partial(pticker.LatitudeFormatter, dms=True)
+        # Cartopy defaults to U+2032/U+2033 prime glyphs for minutes/seconds.
+        # Use them whenever the active font supports them, otherwise use ASCII
+        # fallbacks so that the built-in DMS presets never render missing glyphs.
+        dms_kwargs = {"dms": True, **_get_dms_symbol_kwargs()}
+        registry["dms"] = partial(pticker.DegreeFormatter, **dms_kwargs)
+        registry["dmslon"] = partial(pticker.LongitudeFormatter, **dms_kwargs)
+        registry["dmslat"] = partial(pticker.LatitudeFormatter, **dms_kwargs)
     return registry
 
 

ultraplot/tests/test_geographic.py

@@ -306,6 +306,19 @@ def test_lon0_shifts():
     uplt.close(fig)
 
 
+def test_dms_formatter_symbols_are_default_font_safe():
+    pytest.importorskip("cartopy")
+    formatter = uplt.Formatter("dmslon")
+    label = formatter(1 + 1 / 60 + 1 / 3600)
+    assert formatter._minute_symbol in ("\N{PRIME}", "'")
+    assert formatter._second_symbol in ("\N{DOUBLE PRIME}", '"')
+    assert formatter._minute_symbol in label
+    assert formatter._second_symbol in label
+
+    formatter = uplt.Formatter("dmslon", minute_symbol="m", second_symbol="s")
+    assert formatter(1 + 1 / 60 + 1 / 3600).endswith("1m1sE")
+
+
 @pytest.mark.parametrize(
     "layout, expectations",
     [
@@ -1475,11 +1488,11 @@ def test_dms_used_for_mercator():
     ax.format(land=True, labels=True, lonlocator=limit)
     import matplotlib.ticker as mticker
 
+    minute_symbol = ax[0].gridlines_major.xformatter._minute_symbol
     expectations = (
-        "0°36′E",
-        "113°15′E",
+        f"0°36{minute_symbol}E",
+        f"113°15{minute_symbol}E",
     )
-
     for expectation, tick in zip(expectations, limit):
         a = ax[0].gridlines_major.xformatter(tick)
         b = ax[1].gridlines_major.xformatter(tick)