Update clipboard Qt-bindings for flexiblity and Python3 compatibility

pandas/io/clipboard/__init__.py

@@ -18,7 +18,8 @@
 On Linux, install xclip or xsel via package manager. For example, in Debian:
 sudo apt-get install xclip
 
-Otherwise on Linux, you will need the gtk or PyQt4 modules installed.
+Otherwise on Linux, you will need the gtk or qtpy modules installed.
+qtpy also requires a python-qt-bindings module: PyQt4, PyQt5, PySide, PySide2
 
 gtk and PyQt4 modules are not available for Python 3,
 and this module does not work with PyGObject yet.
@@ -34,9 +35,9 @@
                          init_klipper_clipboard, init_no_clipboard)
 from .windows import init_windows_clipboard
 
-# `import PyQt4` sys.exit()s if DISPLAY is not in the environment.
+# `import qtpy` sys.exit()s if DISPLAY is not in the environment.
 # Thus, we need to detect the presence of $DISPLAY manually
-# and not load PyQt4 if it is absent.
+# and not load qtpy if it is absent.
 HAS_DISPLAY = os.getenv("DISPLAY", False)
 CHECK_CMD = "where" if platform.system() == "Windows" else "which"
 
@@ -68,13 +69,25 @@ def determine_clipboard():
             return init_gtk_clipboard()
 
         try:
-            # Check if PyQt4 is installed
-            import PyQt4  # noqa
+            # qtpy is a small abstraction layer that lets you write applications using a single api call to either PyQt or PySide.
+            # https://pypi.python.org/pypi/QtPy
+            import qtpy  # check if qtpy is installed
         except ImportError:
-            pass
+            # If qtpy isn't installed, fall back on importing PyQt4.
+            try:
+                import PyQt5  # check if PyQt5 is installed
+            except ImportError:
+                try:
+                    import PyQt4  # check if PyQt4 is installed
+                except ImportError:
+                    pass # We want to fail fast for all non-ImportError exceptions.
+                else:
+                    return init_qt_clipboard()
+            else:
+                return init_qt_clipboard()
+
         else:
             return init_qt_clipboard()
-
         if _executable_exists("xclip"):
             return init_xclip_clipboard()
         if _executable_exists("xsel"):

pandas/io/clipboard/clipboards.py

@@ -46,20 +46,24 @@ def paste_gtk():
 
 def init_qt_clipboard():
     # $DISPLAY should exist
-    from PyQt4.QtGui import QApplication
 
-    # use the global instance if it exists
-    app = QApplication.instance() or QApplication([])
+    # Try to import from qtpy, but if that fails try PyQt5 then PyQt4
+    try:
+        from qtpy.QtWidgets import QApplication
+    except:
+        try:
+            from PyQt5.QtWidgets import QApplication
+        except:
+            from PyQt4.QtGui import QApplication
+
+    app = QApplication.instance()
+    if app is None:
+        app = QApplication([])
 
     def copy_qt(text):
         cb = app.clipboard()
         cb.setText(text)
 
-    def paste_qt():
-        cb = app.clipboard()
-        return text_type(cb.text())
-
-    return copy_qt, paste_qt
 
 
 def init_xclip_clipboard():