Respect QT_API even when the backend is not Qt{4,5}{Agg,Cairo}.

anntzer · anntzer · commit 418b9b573c53 · 2018-09-11T10:47:18.000+02:00
- When rcParams["backend"] was not QtXAgg, we previously ignored QT_API.
  Don't do so anymore.  (example: mplcairo.qt...)
- Also add the QtCairo backends to the checks.
diff --git a/lib/matplotlib/backends/qt_compat.py b/lib/matplotlib/backends/qt_compat.py
@@ -24,7 +24,12 @@
 QT_API_PYQTv2 = "PyQt4v2"
 QT_API_PYSIDE = "PySide"
 QT_API_PYQT = "PyQt4"   # Use the old sip v1 API (Py3 defaults to v2).
-QT_API_ENV = os.environ.get('QT_API')
+QT_API_ENV = os.environ.get("QT_API")
+# Mapping of QT_API_ENV to requested binding.  ETS does not support PyQt4v1.
+# (https://github.com/enthought/pyface/blob/master/pyface/qt/__init__.py)
+_ETS = {"pyqt5": QT_API_PYQT5, "pyside2": QT_API_PYSIDE2,
+        "pyqt": QT_API_PYQTv2, "pyside": QT_API_PYSIDE,
+        None: None}
 # First, check if anything is already imported.
 if "PyQt5" in sys.modules:
     QT_API = QT_API_PYQT5
@@ -41,13 +46,13 @@
 # Otherwise, check the QT_API environment variable (from Enthought).  This can
 # only override the binding, not the backend (in other words, we check that the
 # requested backend actually matches).
-elif rcParams["backend"] == "Qt5Agg":
+elif rcParams["backend"] in ["Qt5Agg", "Qt5Cairo"]:
     if QT_API_ENV == "pyqt5":
         dict.__setitem__(rcParams, "backend.qt5", QT_API_PYQT5)
     elif QT_API_ENV == "pyside2":
         dict.__setitem__(rcParams, "backend.qt5", QT_API_PYSIDE2)
     QT_API = dict.__getitem__(rcParams, "backend.qt5")
-elif rcParams["backend"] == "Qt4Agg":
+elif rcParams["backend"] in ["Qt4Agg", "Qt4Cairo"]:
     if QT_API_ENV == "pyqt4":
         dict.__setitem__(rcParams, "backend.qt4", QT_API_PYQTv2)
     elif QT_API_ENV == "pyside":
@@ -56,7 +61,12 @@
 # A non-Qt backend was selected but we still got there (possible, e.g., when
 # fully manually embedding Matplotlib in a Qt app without using pyplot).
 else:
-    QT_API = None
+    try:
+        QT_API = _ETS[QT_API_ENV]
+    except KeyError:
+        raise RuntimeError(
+            "The environment variable QT_API has the unrecognized value {!r};"
+            "valid values are 'pyqt5', 'pyside2', 'pyqt', and 'pyside'")
 
 
 def _setup_pyqt5():
