Changed check_pyqt() to work with qtpy (closes Bitmessage#897)

src/depends.py

@@ -385,21 +385,21 @@ def check_pyqt():
     Here we are checking for PyQt4 with its version, as for it require
     PyQt 4.8 or later.
     """
-    QtCore = try_import(
-        'qtpy.QtCore', 'PyBitmessage requires PyQt 4.8 or later and Qt 4.7 or later.')
+    qtpy = try_import(
+        'qtpy', 'PyBitmessage requires qtpy, PyQt 4.8 or later and Qt 4.7 or later.')
 
-    if not QtCore:
+    if not qtpy:
         return False
 
-    logger.info('PyQt Version: %s', QtCore.PYQT_VERSION_STR)
-    logger.info('Qt Version: %s', QtCore.QT_VERSION_STR)
+    logger.info('PyQt Version: %s', qtpy.PYQT_VERSION)
+    logger.info('Qt Version: %s', qtpy.QT_VERSION)
     passed = True
-    if QtCore.PYQT_VERSION < 0x40800:
+    if qtpy.PYQT_VERSION < '4.8':
         logger.error(
             'This version of PyQt is too old. PyBitmessage requries'
             ' PyQt 4.8 or later.')
         passed = False
-    if QtCore.QT_VERSION < 0x40700:
+    if qtpy.QT_VERSION < '4.7':
         logger.error(
             'This version of Qt is too old. PyBitmessage requries'
             ' Qt 4.7 or later.')