IPython Notebook: Open/select file with GUI (Qt Dialog)
When you perform the same analysis in a notebook on different data files, may be handy to graphically select a data file.
In my python scripts I usually implement a QT dialog that returns the file-name of the selected file:
from PySide import QtCore, QtGui
def gui_fname(dir=None):
    """Select a file via a dialog and return the file name.
    """
    if dir is None: dir ='./'
    fname = QtGui.QFileDialog.getOpenFileName(None, "Select data file...", 
            dir, filter="All files (*);; SM Files (*.sm)")
    return fname[0]
However, running this function from an notebook
full_fname = gui_fname()
causes the kernel to die (and restart):
Interestingly, puttying this 3 command in 3 separate cells works
%matplotlib qt
full_fname = gui_fname()
%matplotlib inline
but when I put those commands in one single cell the kernel dies again.
 This prevents to create a function like gui_fname_ipynb() that transparently allows selecting a file with a GUI.  
For convenience, I created a notebook illustrating the problem:
Any suggestion on how to execute a dialog for file selection from within an IPython Notebook?
This behaviour was a bug in IPython:
https://github.com/ipython/ipython/issues/4997
that was fixed here:
https://github.com/ipython/ipython/pull/5077
The function to open a gui dialog should work on current master and on the oncoming 2.0 release.
To date, the last 1.x version (1.2.1) does not include a backport of the fix.
EDIT: The example code still crashes IPython 2.x, see this issue.
Using Anaconda 5.0.0 on windows (Python 3.6.2, IPython 6.1.0), the following two options are both working for me.
OPTION 1: Entirely in a Jupyter notebook:
CELL 1:
%gui qt
from PyQt5.QtWidgets import QFileDialog
def gui_fname(dir=None):
    """Select a file via a dialog and return the file name."""
    if dir is None: dir ='./'
    fname = QFileDialog.getOpenFileName(None, "Select data file...", 
                dir, filter="All files (*);; SM Files (*.sm)")
    return fname[0]
CELL 2:
gui_fname()
 This is working for me but it seems a bit...fragile.  If I combine these two things into the same cell, it crashes.  Or if I omit the %gui qt , it crashes.  If I "restart kernel and run all cells", it doesn't work.  So I kinda like this other option...  
MORE RELIABLE OPTION: Separate script that opens dialog box in a new process
(Based on mkrog code here.)
 PUT THE FOLLOWING IN A SEPARATE PYTHON SCRIPT CALLED blah.py :  
from sys import executable, argv
from subprocess import check_output
from PyQt5.QtWidgets import QFileDialog, QApplication
def gui_fname(directory='./'):
    """Open a file dialog, starting in the given directory, and return
    the chosen filename"""
    # run this exact file in a separate process, and grab the result
    file = check_output([executable, __file__, directory])
    return file.strip()
if __name__ == "__main__":
    directory = argv[1]
    app = QApplication([directory])
    fname = QFileDialog.getOpenFileName(None, "Select a file...", 
            directory, filter="All files (*)")
    print(fname[0])
...AND IN YOUR JUPYTER NOTEBOOK
import blah
blah.gui_fname()
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