modify environment to choose binding

the Example App allows the user to choose a binding and a graphics
system to use to execute an example.

issue 1: setGraphicsSystem is obsolete and the method no longer exists.
thus selecting a graphics system causes an error.

issue 2: the choice of binding to use is passed as an extra command
line argument to be parsed by initExample. this is problematic for
examples that use argparse, such as VideoSpeedTest.py

issue 3: if the user has set PYQTGRAPH_QT_LIB, that takes precedence
over the choice made in the Example App.

this patch fixes the above 3 issues by setting PYQTGRAPH_QT_LIB in
the child process' environment and removing the old parsing of the
command line arguments

examples/ExampleApp.py

@@ -344,18 +344,15 @@ class ExampleLoader(QtGui.QMainWindow):
 
     def loadFile(self, edited=False):
 
-        extra = []
         qtLib = str(self.ui.qtLibCombo.currentText())
-        gfxSys = str(self.ui.graphicsSystemCombo.currentText())
 
+        env = None
         if qtLib != 'default':
-            extra.append(qtLib.lower())
-        elif gfxSys != 'default':
-            extra.append(gfxSys)
+            env = dict(os.environ, PYQTGRAPH_QT_LIB=qtLib)
 
         if edited:
             path = os.path.abspath(os.path.dirname(__file__))
-            proc = subprocess.Popen([sys.executable, '-'] + extra, stdin=subprocess.PIPE, cwd=path)
+            proc = subprocess.Popen([sys.executable, '-'], stdin=subprocess.PIPE, cwd=path, env=env)
             code = str(self.ui.codeView.toPlainText()).encode('UTF-8')
             proc.stdin.write(code)
             proc.stdin.close()
@@ -364,9 +361,14 @@ class ExampleLoader(QtGui.QMainWindow):
             if fn is None:
                 return
             if sys.platform.startswith('win'):
-                os.spawnl(os.P_NOWAIT, sys.executable, '"'+sys.executable+'"', '"' + fn + '"', *extra)
+                args = [os.P_NOWAIT, sys.executable, '"'+sys.executable+'"', '"' + fn + '"']
             else:
-                os.spawnl(os.P_NOWAIT, sys.executable, sys.executable, fn, *extra)
+                args = [os.P_NOWAIT, sys.executable, sys.executable, fn]
+            if env is None:
+                os.spawnl(*args)
+            else:
+                args.append(env)
+                os.spawnle(*args)
 
     def showFile(self):
         fn = self.currentFile()

examples/VideoSpeedTest.py

@@ -6,6 +6,9 @@ it is being scaled and/or converted by lookup table, and whether OpenGL
 is used by the view widget
 """
 
+## Add path to library (just for examples; you do not need this)
+import initExample
+
 import argparse
 import sys
 

examples/initExample.py

@@ -20,25 +20,8 @@ if not hasattr(sys, 'frozen'):
                 sys.path.remove(p)
                 sys.path.insert(0, p)
 
-## should force example to use PySide instead of PyQt
-for module in ['PyQt5', 'PySide2', 'PySide6', 'PyQt6']:
-    if module.lower() in sys.argv:
-        QtGui = importlib.import_module(module + '.QtGui')
-        break
-else:
-    from pyqtgraph.Qt import QtGui
-
 import pyqtgraph as pg    
-    
-## Force use of a specific graphics system
-use_gs = 'default'
-for gs in ['raster', 'native', 'opengl']:
-    if gs in sys.argv:
-        use_gs = gs
-        QtGui.QApplication.setGraphicsSystem(gs)
-        break
-
-print("Using %s (%s graphics system)" % (pg.Qt.QT_LIB, use_gs))
+print("Using", pg.Qt.QT_LIB)
 
 ## Enable fault handling to give more helpful error messages on crash. 
 ## Only available in python 3.3+