allow subfigure formatting (#167)

* Allow subfigure formatting

Author: cvanelteren

ultraplot/figure.py

@@ -1684,14 +1684,19 @@ def format(
             for cls, sig in paxes.Axes._format_signatures.items()
         }
         classes = set()  # track used dictionaries
-        for ax in axs:
+        for number, ax in enumerate(axs):
+            number = number + 1  # number from 1
+            store_old_number = ax.number
+            if ax.number != number:
+                ax.number = number
             kw = {
                 key: value
                 for cls, kw in kws.items()
                 for key, value in kw.items()
                 if isinstance(ax, cls) and not classes.add(cls)
             }
             ax.format(rc_kw=rc_kw, rc_mode=rc_mode, skip_figure=True, **kw, **kwargs)
+            ax.number = store_old_number
 
         # Warn unused keyword argument(s)
         kw = {

ultraplot/tests/test_axes.py

@@ -175,3 +175,15 @@ def test_twin_axes_3():
         ax.format(ylabel="%s Thing" % color, ycolor=color)
     axs[0].format(xlabel="xlabel")
     return fig
+
+
+def test_subset_format():
+    fig, axs = uplt.subplots(nrows=1, ncols=3)
+    axs[1:].format(title=["a", "b"])  # allowed
+    # Subset formatting
+    axs[1:].format(title=["c", "d", "e"])  # allowed but does not use e
+    assert axs[-1].get_title() == "d"
+    assert axs[0].get_title() == ""
+    # Shorter than number of axs
+    with pytest.raises(ValueError):
+        axs.format(title=["a"])