Fix backend detection in headless mode.

anntzer · anntzer · commit f0f351c3b6d1 · 2017-11-17T18:45:47.000-08:00
diff --git a/lib/matplotlib/backends/__init__.py b/lib/matplotlib/backends/__init__.py
@@ -5,6 +5,7 @@
 
 import importlib
 import logging
+import os
 import sys
 import traceback
 
@@ -17,12 +18,14 @@
 
 
 def _get_current_event_loop():
-    """Return the currently running event loop if any, or None.
+    """Return the currently running event loop if any, or "headless", or None.
+
+    "headless" indicates that no event loop can be started.
 
     Returns
     -------
     Optional[str]
-        A value in {"qt5", "qt4", "gtk3", "gtk2", "tk", None}
+        A value in {"qt5", "qt4", "gtk3", "gtk2", "tk", "headless", None}
     """
     # FIXME Add detection of OSX event loop.
     QtWidgets = sys.modules.get("PyQt5.QtWidgets")
@@ -43,6 +46,8 @@ def _get_current_event_loop():
                        and frame.f_code.co_name == "mainloop"
                        for frame in sys._current_frames().values()):
         return "tk"
+    if sys.platform.startswith("linux") and not os.environ.get("DISPLAY"):
+        return "headless"
 
 
 def pylab_setup(name=None):
@@ -85,9 +90,10 @@ def pylab_setup(name=None):
     if isinstance(name, list):
         for n in name:
             try:
+                _log.info("Trying to load backend %s.", n)
                 return pylab_setup(n)
-            except ImportError:
-                pass
+            except ImportError as exc:
+                _log.info("Loading backend %s failed: %s", n, exc)
         else:
             raise ValueError("No suitable backend among {}".format(name))
 
@@ -96,7 +102,7 @@ def pylab_setup(name=None):
 
     backend_mod = importlib.import_module(backend_name)
     Backend = type(str("Backend"), (_Backend,), vars(backend_mod))
-    _log.info('backend %s version %s', name, Backend.backend_version)
+    _log.info("Loaded backend %s version %s.", name, Backend.backend_version)
 
     required_event_loop = Backend.required_event_loop
     current_event_loop = _get_current_event_loop()
diff --git a/lib/matplotlib/backends/backend_gtk.py b/lib/matplotlib/backends/backend_gtk.py
@@ -17,7 +17,8 @@
     import gobject
     import gtk; gdk = gtk.gdk
     import pango
-except ImportError:
+except (ImportError, AttributeError):
+    # AttributeError occurs when getting gtk.gdk if gi is already imported.
     raise ImportError("Gtk* backend requires pygtk to be installed.")
 
 pygtk_version_required = (2,4,0)
diff --git a/lib/matplotlib/backends/backend_gtk3.py b/lib/matplotlib/backends/backend_gtk3.py
@@ -50,13 +50,18 @@
 # see http://groups.google.com/groups?q=screen+dpi+x11&hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&selm=7077.26e81ad5%40swift.cs.tcd.ie&rnum=5 for some info about screen dpi
 PIXELS_PER_INCH = 96
 
-cursord = {
-    cursors.MOVE          : Gdk.Cursor.new(Gdk.CursorType.FLEUR),
-    cursors.HAND          : Gdk.Cursor.new(Gdk.CursorType.HAND2),
-    cursors.POINTER       : Gdk.Cursor.new(Gdk.CursorType.LEFT_PTR),
-    cursors.SELECT_REGION : Gdk.Cursor.new(Gdk.CursorType.TCROSS),
-    cursors.WAIT          : Gdk.Cursor.new(Gdk.CursorType.WATCH),
-    }
+try:
+    cursord = {
+        cursors.MOVE          : Gdk.Cursor.new(Gdk.CursorType.FLEUR),
+        cursors.HAND          : Gdk.Cursor.new(Gdk.CursorType.HAND2),
+        cursors.POINTER       : Gdk.Cursor.new(Gdk.CursorType.LEFT_PTR),
+        cursors.SELECT_REGION : Gdk.Cursor.new(Gdk.CursorType.TCROSS),
+        cursors.WAIT          : Gdk.Cursor.new(Gdk.CursorType.WATCH),
+        }
+except TypeError as exc:
+    # Happens when running headless.  Convert to ImportError to cooperate with
+    # backend switching.
+    raise ImportError(exc)
 
 
 class TimerGTK3(TimerBase):
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -4,7 +4,6 @@
 
 import functools
 import os
-import re
 import signal
 import sys
 from six import unichr
@@ -116,10 +115,8 @@ def _create_qApp():
                     is_x11_build = False
             else:
                 is_x11_build = hasattr(QtGui, "QX11Info")
-            if is_x11_build:
-                display = os.environ.get('DISPLAY')
-                if display is None or not re.search(r':\d', display):
-                    raise RuntimeError('Invalid DISPLAY variable')
+            if is_x11_build and not os.environ.get("DISPLAY"):
+                raise RuntimeError("No DISPLAY variable")
 
             qApp = QtWidgets.QApplication([b"matplotlib"])
             qApp.lastWindowClosed.connect(qApp.quit)
diff --git a/lib/matplotlib/backends/qt_compat.py b/lib/matplotlib/backends/qt_compat.py
@@ -112,17 +112,17 @@
             QT_API = QT_API_PYSIDE2
         else:
             QT_API = QT_API_PYSIDE
-        cond = ("Could not import sip; falling back on PySide\n"
-                "in place of PyQt4 or PyQt5.\n")
+        cond = ("Could not import sip; falling back on PySide in place of "
+                "PyQt4 or PyQt5.")
         _log.info(cond)
 
 if _sip_imported:
     if QT_API == QT_API_PYQTv2:
         if QT_API_ENV == 'pyqt':
             cond = ("Found 'QT_API=pyqt' environment variable. "
-                    "Setting PyQt4 API accordingly.\n")
+                    "Setting PyQt4 API accordingly. ")
         else:
-            cond = "PyQt API v2 specified."
+            cond = "PyQt API v2 specified. "
         try:
             sip.setapi('QString', 2)
         except:
@@ -201,7 +201,7 @@ def _getSaveFileName(*args, **kwargs):
         from PySide import QtCore, QtGui, __version__, __version_info__
     except ImportError:
         raise ImportError(
-            "Matplotlib qt-based backends require an external PyQt4, PyQt5,\n"
+            "Matplotlib qt-based backends require an external PyQt4, PyQt5, "
             "PySide or PySide2 package to be installed, but it was not found.")
 
     if __version_info__ < (1, 0, 3):
diff --git a/src/_macosx.m b/src/_macosx.m
@@ -3056,15 +3056,15 @@ static bool verify_framework(void)
      && GetCurrentProcess(&psn)==noErr
      && SetFrontProcess(&psn)==noErr) return true;
 #endif
-    PyErr_SetString(PyExc_RuntimeError,
+    PyErr_SetString(PyExc_ImportError,
         "Python is not installed as a framework. The Mac OS X backend will "
         "not be able to function correctly if Python is not installed as a "
         "framework. See the Python documentation for more information on "
         "installing Python as a framework on Mac OS X. Please either reinstall "
         "Python as a framework, or try one of the other backends. If you are "
-        "using (Ana)Conda please install python.app and replace the use of 'python' "
-        "with 'pythonw'. See 'Working with Matplotlib on OSX' "
-        "in the Matplotlib FAQ for more information.");
+        "using (Ana)Conda please install python.app and replace the use of "
+        "'python' with 'pythonw'. See 'Working with Matplotlib on OSX' in the "
+        "Matplotlib FAQ for more information.");
     return false;
 }
 
