Fix xvals for datetime axis

labellines/core.py

@@ -3,6 +3,7 @@
 
 import matplotlib.pyplot as plt
 import numpy as np
+from datetime import datetime
 from matplotlib.container import ErrorbarContainer
 from matplotlib.dates import DateConverter, num2date
 from matplotlib.lines import Line2D
@@ -186,18 +187,34 @@ def labelLines(
     if isinstance(xvals, tuple) and len(xvals) == 2:
         xmin, xmax = xvals
         xscale = ax.get_xscale()
+
+        # Convert datetime objects to numeric values for linspace/geomspace
+        x_is_datetime = isinstance(xmin, datetime) or isinstance(xmax, datetime)
+        if x_is_datetime:
+            if not isinstance(xmin, datetime) or not isinstance(xmax, datetime):
+                raise ValueError(
+                    f"Cannot mix datetime and numeric values in xvals: {xvals}"
+                )
+            xmin = plt.matplotlib.dates.date2num(xmin)
+            xmax = plt.matplotlib.dates.date2num(xmax)
+
         if xscale == "log":
             xvals = np.geomspace(xmin, xmax, len(all_lines) + 2)[1:-1]
         else:
             xvals = np.linspace(xmin, xmax, len(all_lines) + 2)[1:-1]
 
+        # Convert numeric values back to datetime objects
+        if x_is_datetime:
+            xvals = plt.matplotlib.dates.num2date(xvals)
+
         # Build matrix line -> xvalue
         ok_matrix = np.zeros((len(all_lines), len(all_lines)), dtype=bool)
 
         for i, line in enumerate(all_lines):
             xdata, _ = normalize_xydata(line)
             minx, maxx = min(xdata), max(xdata)
             for j, xv in enumerate(xvals):  # type: ignore
+                xv = line.convert_xunits(xv)
                 ok_matrix[i, j] = minx < xv < maxx
 
         # If some xvals do not fall in their corresponding line,
@@ -224,6 +241,8 @@ def labelLines(
         # Move xlabel if it is outside valid range
         xdata, _ = normalize_xydata(line)
         xmin, xmax = min(xdata), max(xdata)
+        xv = line.convert_xunits(xv)
+
         if not (xmin <= xv <= xmax):
             warnings.warn(
                 (

labellines/test.py

@@ -164,7 +164,7 @@ def test_dateaxis_advanced(setup_mpl):
     ax.xaxis.set_major_locator(DayLocator())
     ax.xaxis.set_major_formatter(DateFormatter("%Y-%m-%d"))
 
-    labelLines(ax.get_lines())
+    labelLines(ax.get_lines(), xvals=(dates[0], dates[-1]))
     return plt.gcf()