PyQt5 based qtpy fallback

src/bitmessageqt/support.py

@@ -144,7 +144,7 @@ def createSupportMessage(myapp):
     opensslversion = "%s (Python internal), %s (external for PyElliptic)" % (
         ssl.OPENSSL_VERSION, OpenSSL._version)
 
-    qtapi = os.environ['QT_API']
+    qtapi = os.environ.get('QT_API', 'fallback')
 
     frozen = "N/A"
     if paths.frozen:

src/depends.py

@@ -3,6 +3,8 @@ Utility functions to check the availability of dependencies
 and suggest how it may be installed
 """
 
+# flake8: noqa:E402
+
 import sys
 
 # Only really old versions of Python don't have sys.hexversion. We don't
@@ -365,9 +367,13 @@ def check_pyqt():
     PyQt 4.8 or later.
     """
     # pylint: disable=no-member
-    qtpy = try_import(
-        'qtpy',
-        'PyBitmessage requires qtpy, PyQt 4.8 or later and Qt 4.7 or later.')
+    try:
+        from fallback import qtpy
+    except ImportError:
+        logger.error(
+            'PyBitmessage requires qtpy, PyQt 4.8 or later and Qt 4.7 or later.'
+        )
+        qtpy = None
 
     if not qtpy:
         return False

src/fallback/__init__.py

@@ -30,3 +30,30 @@ else:
         if data:
             hasher.update(data)
         return hasher
+
+try:
+    import qtpy
+except ImportError:
+    try:
+        from PyQt5 import QtCore, QtGui, QtWidgets, QtNetwork, uic
+    except ImportError:
+        qtpy = None
+    else:
+        import sys
+        import types
+
+        QtCore.Signal = QtCore.pyqtSignal
+        context = {
+            'API': 'pyqt5',  # for tr
+            'PYQT_VERSION': QtCore.PYQT_VERSION_STR,
+            'QT_VERSION': QtCore.QT_VERSION_STR,
+            'QtCore': QtCore,
+            'QtGui': QtGui,
+            'QtWidgets': QtWidgets,
+            'QtNetwork': QtNetwork,
+            'uic': uic
+        }
+        qtpy = types.ModuleType(
+            'qtpy', 'PyQt5 based dynamic fallback for qtpy')
+        qtpy.__dict__.update(context)
+        sys.modules['qtpy'] = qtpy

src/tr.py

@@ -12,6 +12,7 @@ def _tr_dummy(context, text, disambiguation=None, n=None):
 
 if state.enableGUI and not state.curses:
     try:
+        from fallback import qtpy  # noqa:F401
         from qtpy import QtWidgets, QtCore, API
     except ImportError:
         _translate = _tr_dummy