Update clipboard Qt-bindings for flexiblity and Python3 compatibility (#17723)

Author: dvincentwest

ci/requirements-3.6_BUILD_TEST.sh

@@ -4,4 +4,4 @@ source activate pandas
 
 echo "install 36 BUILD_TEST"
 
-conda install -n pandas -c conda-forge pyarrow dask
+conda install -n pandas -c conda-forge pyarrow dask pyqt qtpy

doc/source/install.rst

@@ -251,12 +251,13 @@ Optional Dependencies
 * `Jinja2 <http://jinja.pocoo.org/>`__: Template engine for conditional HTML formatting.
 * `s3fs <http://s3fs.readthedocs.io/>`__: necessary for Amazon S3 access (s3fs >= 0.0.7).
 * `blosc <https://pypi.python.org/pypi/blosc>`__: for msgpack compression using ``blosc``
-* One of `PyQt4
-  <http://www.riverbankcomputing.com/software/pyqt/download>`__, `PySide
-  <http://qt-project.org/wiki/Category:LanguageBindings::PySide>`__, `pygtk
-  <http://www.pygtk.org/>`__, `xsel
-  <http://www.vergenet.net/~conrad/software/xsel/>`__, or `xclip
-  <https://github.com/astrand/xclip/>`__: necessary to use
+* One of
+  `qtpy  <https://github.com/spyder-ide/qtpy>`__ (requires PyQt or PySide),
+  `PyQt5 <https://www.riverbankcomputing.com/software/pyqt/download5>`__,
+  `PyQt4 <http://www.riverbankcomputing.com/software/pyqt/download>`__,
+  `pygtk <http://www.pygtk.org/>`__,
+  `xsel <http://www.vergenet.net/~conrad/software/xsel/>`__, or
+  `xclip <https://github.com/astrand/xclip/>`__: necessary to use
   :func:`~pandas.read_clipboard`. Most package managers on Linux distributions will have ``xclip`` and/or ``xsel`` immediately available for installation.
 * For Google BigQuery I/O - see `here <https://pandas-gbq.readthedocs.io/en/latest/install.html#dependencies>`__
 

doc/source/io.rst

@@ -3053,7 +3053,7 @@ We can see that we got the same content back, which we had earlier written to th
 
 .. note::
 
-   You may need to install xclip or xsel (with gtk or PyQt4 modules) on Linux to use these methods.
+   You may need to install xclip or xsel (with gtk, PyQt5, PyQt4 or qtpy) on Linux to use these methods.
 
 .. _io.pickle:
 

doc/source/whatsnew/v0.22.0.txt

@@ -44,6 +44,7 @@ Other Enhancements
 - :class:`pandas.io.formats.style.Styler` now has method ``hide_columns()`` to determine whether columns will be hidden in output (:issue:`14194`)
 - Improved wording of ``ValueError`` raised in :func:`to_datetime` when ``unit=`` is passed with a non-convertible value (:issue:`14350`)
 - :func:`Series.fillna` now accepts a Series or a dict as a ``value`` for a categorical dtype (:issue:`17033`)
+- :func:`pandas.read_clipboard` updated to use qtpy, falling back to PyQt5 and then PyQt4, adding compatibility with Python3 and multiple python-qt bindings (:issue:`17722`)
 
 .. _whatsnew_0220.api_breaking:
 

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, qtpy or PyQt 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"
 
@@ -68,9 +69,23 @@ 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  # noqa
         except ImportError:
+            # If qtpy isn't installed, fall back on importing PyQt5, or PyQt5
+            try:
+                import PyQt5  # noqa
+            except ImportError:
+                try:
+                    import PyQt4  # noqa
+                except ImportError:
+                    pass  # fail fast for all non-ImportError exceptions.
+                else:
+                    return init_qt_clipboard()
+            else:
+                return init_qt_clipboard()
             pass
         else:
             return init_qt_clipboard()

pandas/io/clipboard/clipboards.py

@@ -46,10 +46,19 @@ 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 ImportError:
+        try:
+            from PyQt5.QtWidgets import QApplication
+        except ImportError:
+            from PyQt4.QtGui import QApplication
+
+    app = QApplication.instance()
+    if app is None:
+        app = QApplication([])
 
     def copy_qt(text):
         cb = app.clipboard()