Figure.legend: Support passing a StringIO object as the legend specification

pygmt/src/legend.py

@@ -2,6 +2,7 @@
 legend - Plot a legend.
 """
 
+import io
 import pathlib
 
 from pygmt.clib import Session
@@ -30,7 +31,7 @@
 @kwargs_to_strings(R="sequence", c="sequence_comma", p="sequence")
 def legend(
     self,
-    spec: str | pathlib.PurePath | None = None,
+    spec: str | pathlib.PurePath | io.StringIO | None = None,
     position="JTR+jTR+o0.2c",
     box="+gwhite+p1p",
     **kwargs,
@@ -57,6 +58,7 @@ def legend(
           file
         - A string or a :class:`pathlib.PurePath` object pointing to the legend
           specification file
+        - A :class:`io.StringIO` object containing the legend specification.
 
         See :gmt-docs:`legend.html` for the definition of the legend specification.
     {projection}
@@ -89,10 +91,11 @@ def legend(
             kwargs["F"] = box
 
     kind = data_kind(spec)
-    if kind not in {"vectors", "file"}:  # kind="vectors" means spec is None
+    if kind not in {"vectors", "file", "stringio"}:  # kind="vectors" means spec is None
         raise GMTInvalidInput(f"Unrecognized data type: {type(spec)}")
     if kind == "file" and is_nonstr_iter(spec):
         raise GMTInvalidInput("Only one legend specification file is allowed.")
 
     with Session() as lib:
-        lib.call_module(module="legend", args=build_arg_list(kwargs, infile=spec))
+        with lib.virtualfile_in(data=spec, required_data=False) as vintbl:
+            lib.call_module(module="legend", args=build_arg_list(kwargs, infile=vintbl))

pygmt/tests/test_legend.py

@@ -2,6 +2,7 @@
 Test Figure.legend.
 """
 
+import io
 from pathlib import Path
 
 import pytest
@@ -100,6 +101,18 @@ def test_legend_specfile(legend_spec):
         fig = Figure()
         fig.basemap(projection="x6i", region=[0, 1, 0, 1], frame=True)
         fig.legend(specfile.name, position="JTM+jCM+w5i")
+        return fig
+
+
+@pytest.mark.mpl_image_compare(filename="test_legend_specfile.png")
+def test_legend_stringio(legend_spec):
+    """
+    Test passing a legend specification via an io.StringIO object.
+    """
+    spec = io.StringIO(legend_spec)
+    fig = Figure()
+    fig.basemap(projection="x6i", region=[0, 1, 0, 1], frame=True)
+    fig.legend(spec, position="JTM+jCM+w5i")
     return fig