fix #7908

zhoubecky · zhoubecky · commit 0e024ff72a23 · 2018-03-19T11:57:35.000-04:00
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -182,13 +182,20 @@ def show(cls, block=None):
         is ``None`` and we are neither in IPython's ``%pylab`` mode, nor in
         `interactive` mode.
         """
-        if cls.mainloop is None:
-            return
         managers = Gcf.get_all_fig_managers()
         if not managers:
             return
         for manager in managers:
-            manager.show()
+            try:
+                manager.show()
+            except NonGuiException:
+                warnings.warn(
+                    ('matplotlib is currently using %s, which is a ' +
+                     'non-GUI backend, so cannot show the figure.')
+                    % get_backend())
+                return
+        if cls.mainloop is None:
+            return
         if block is None:
             # Hack: Are we in IPython's pylab mode?
             from matplotlib import pyplot
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -24,6 +24,7 @@
 from matplotlib import rcParams
 from matplotlib import docstring
 from matplotlib import __version__ as _mpl_version
+from matplotlib import get_backend
 
 import matplotlib.artist as martist
 from matplotlib.artist import Artist, allow_rasterization
@@ -431,7 +432,7 @@ def show(self, warn=True):
 
         Parameters
         ----------
-        warm : bool
+        warn : bool
             If ``True``, issue warning when called on a non-GUI backend
 
         Notes
@@ -454,10 +455,10 @@ def show(self, warn=True):
             except NonGuiException:
                 pass
         if warn:
-            import warnings
             warnings.warn(
-                "matplotlib is currently using a non-GUI backend, "
-                "so cannot show the figure")
+                ('matplotlib is currently using %s, which is a ' +
+                 'non-GUI backend, so cannot show the figure.')
+                % get_backend())
 
     def _get_axes(self):
         return self._axstack.as_list()
diff --git a/lib/matplotlib/tests/test_backend_bases.py b/lib/matplotlib/tests/test_backend_bases.py
@@ -9,6 +9,7 @@
 import os
 import shutil
 import tempfile
+import pytest
 
 
 def test_uses_per_path():
@@ -77,3 +78,21 @@ def test_get_default_filename_already_exists():
         assert filename == 'image-1.png'
     finally:
         shutil.rmtree(test_dir)
+
+
+@pytest.mark.backend('pdf')
+def test_non_gui_warning():
+    plt.subplots()
+    with pytest.warns(UserWarning) as rec:
+        plt.show()
+        assert len(rec) == 1
+        assert 'matplotlib is currently using pdf, ' \
+               'which is a non-GUI backend' \
+               in str(rec[0].message)
+
+    with pytest.warns(UserWarning) as rec:
+        plt.gcf().show()
+        assert len(rec) == 1
+        assert 'matplotlib is currently using pdf, ' \
+               'which is a non-GUI backend' \
+               in str(rec[0].message)
