Deprecate the useless switch_backend_warn parameter to matplotlib.test.

anntzer · anntzer · commit 57a7f52baf18 · 2019-04-12T11:30:24.000+02:00
matplotlib.test always calls matplotlib.use() with force set to its
default value of True, which means that the warn parameter has no
effect.  So just don't bother passing it.

Also slightly reorder the logic in use() to make this more apparent (I
think?).
diff --git a/doc/api/next_api_changes/2019-04-12-AL.rst b/doc/api/next_api_changes/2019-04-12-AL.rst
@@ -0,0 +1,5 @@
+Deprecations
+````````````
+
+The ``switch_backend_warn`` parameter to ``matplotlib.test`` has no effect and
+is deprecated.
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
@@ -1262,7 +1262,6 @@ def use(backend, warn=False, force=True):
         If True and not *force*, warn that the call will have no effect if
         this is called after pyplot has been imported and a backend is set up.
 
-
     force : bool, optional, default: True
         If True, attempt to switch the backend.   An ImportError is raised if
         an interactive backend is selected, but another interactive
@@ -1281,20 +1280,17 @@ def use(backend, warn=False, force=True):
     elif 'matplotlib.pyplot' in sys.modules:
         # pyplot has already been imported (which triggered backend selection)
         # and the requested backend is different from the current one.
-
-        # If we are going to force the switch, never warn, else, if warn
-        # is True, then direct users to `plt.switch_backend`
-        if (not force) and warn:
-            cbook._warn_external(
-                "matplotlib.pyplot has already been imported, "
-                "this call will have no effect.")
-
-        # if we are going to force switching the backend, pull in
-        # `switch_backend` from pyplot.  This will only happen if
-        # pyplot is already imported.
         if force:
+            # if we are going to force switching the backend, pull in
+            # `switch_backend` from pyplot (which is already imported).
             from matplotlib.pyplot import switch_backend
             switch_backend(name)
+        elif warn:
+            # Only if we are not going to force the switch *and* warn is True,
+            # then direct users to `plt.switch_backend`.
+            cbook._warn_external(
+                "matplotlib.pyplot has already been imported, "
+                "this call will have no effect.")
     else:
         # Finally if pyplot is not imported update both rcParams and
         # rcDefaults so restoring the defaults later with rcdefaults
@@ -1385,6 +1381,7 @@ def _init_tests():
         raise
 
 
+@cbook._delete_parameter("3.2", "switch_backend_warn")
 def test(verbosity=None, coverage=False, switch_backend_warn=True,
          recursionlimit=0, **kwargs):
     """Run the matplotlib test suite."""
@@ -1426,7 +1423,7 @@ def test(verbosity=None, coverage=False, switch_backend_warn=True,
         retcode = pytest.main(args, **kwargs)
     finally:
         if old_backend.lower() != 'agg':
-            use(old_backend, warn=switch_backend_warn)
+            use(old_backend)
         if recursionlimit:
             sys.setrecursionlimit(old_recursionlimit)
 
diff --git a/tests.py b/tests.py
@@ -45,6 +45,5 @@
 
     print('Python byte-compilation optimization level:', sys.flags.optimize)
 
-    retcode = test(argv=extra_args, switch_backend_warn=False,
-                   recursionlimit=args.recursionlimit)
+    retcode = test(argv=extra_args, recursionlimit=args.recursionlimit)
     sys.exit(retcode)
