A template for loading .ui files from QtDesigner and integrating them with Maya 2016.5 or below.

bm_qtDesignerTemplate.py

import sys
import os

from PySide import QtCore, QtGui, QtUiTools
import shiboken

import maya.cmds as cmds
import maya.OpenMayaUI as MayaUI

"""
    Code template for loading .ui files into Maya courtesy of Brian Kortbus
    http://www.briankortbus.com/single-post/2016/11/09/UI-Files-in-Maya-2016-PySide---Part-2
"""

# Where is this script?
SCRIPT_LOC = os.path.split(__file__)[0]


def loadUiWidget(uifilename, parent=None):
    """Properly Loads and returns UI files - by BarryPye on stackOverflow"""
    loader = QtUiTools.QUiLoader()
    uifile = QtCore.QFile(uifilename)
    uifile.open(QtCore.QFile.ReadOnly)
    ui = loader.load(uifile, parent)
    uifile.close()
    return ui


# Call this function inside of Maya to run the script:
def runMayaTemplateUi():
    """Command within Maya to run this script"""
    if not (cmds.window("templateUi", exists=True)):
        TemplateUi()
    else:
        sys.stdout.write("Tool is already open!\n")


class TemplateUi(QtGui.QMainWindow):
    """A bare minimum UI class - showing a .ui file inside Maya 2016"""

    def __init__(self):
        mainUI = SCRIPT_LOC + "\\qtDesignerDoc.ui"
        MayaMain = shiboken.wrapInstance(long(MayaUI.MQtUtil.mainWindow()), QtGui.QWidget)
        super(TemplateUi, self).__init__(MayaMain)

        # main window load / settings
        self.MainWindowUI = loadUiWidget(mainUI, MayaMain)
        self.MainWindowUI.setAttribute(QtCore.Qt.WA_DeleteOnClose, True)
        self.MainWindowUI.destroyed.connect(self.onExitCode)
        self.MainWindowUI.show()

        self.makeConnections()

    def makeConnections(self):
        # the lambda: is (in my words) a handy way to pass an argument to our function without python running it.
        self.MainWindowUI.addCube_btn.clicked.connect(lambda: self.someFunction("I'm a function!"))

    def onExitCode(self):
        """Do this when the script is closed"""
        sys.stdout.write("UI successfully closed\n")

    def someFunction(self, someArg):
        print someArg