options_widget.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>ScatterWidget</class>
 <widget class="QWidget" name="ScatterWidget">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>287</width>
    <height>230</height>
   </rect>
  </property>
     <layout class="QVBoxLayout" name="verticalLayout">
      <item>
       <widget class="QComboBox" name="xAxisComboBox">
       </widget>
      </item>
     </layout>
 </widget>
 <resources/>
 <connections/>
</ui>

test_pyside.py

import os

from PySide import QtGui
from PySide.QtUiTools import QUiLoader


class Widget(QtGui.QWidget):

    def __init__(self, parent=None):
        super(Widget, self).__init__(parent=parent)
        loader = QUiLoader()
        self.ui = loader.load('options_widget.ui', self)


class MainTest(QtGui.QWidget):

    def __init__(self, parent=None):
        super(MainTest, self).__init__(parent=parent)
        self.layout = QtGui.QVBoxLayout()
        self.setLayout(self.layout)

    def add_widget(self):
        self.layout.addWidget(Widget())


app = QtGui.QApplication([])

main = MainTest()
main.show()
main.add_widget()

app.exec_()