AttributeError: 'QSlider' object has no attribute 'subtractStep' - python-2.7

Question

I am getting an error when I try to run this code:
# -*- coding: utf-8 -*-
# Form implementation generated from reading ui file 'scaler_gui_3.ui'
#
# Created: Thu May 14 13:05:28 2015
# by: PyQt4 UI code generator 4.11.3
#
# WARNING! All changes made in this file will be lost!
from PyQt4 import QtCore, QtGui
try:
_fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
def _fromUtf8(s):
return s
try:
_encoding = QtGui.QApplication.UnicodeUTF8
def _translate(context, text, disambig):
return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
def _translate(context, text, disambig):
return QtGui.QApplication.translate(context, text, disambig)
class Ui_Form(object):
def setupUi(self, Form):
Form.setObjectName(_fromUtf8("Form"))
Form.resize(270, 219)
self.gridLayout_2 = QtGui.QGridLayout(Form)
self.gridLayout_2.setObjectName(_fromUtf8("gridLayout_2"))
self.horizontalSliderFrames = QtGui.QSlider(Form)
self.horizontalSliderFrames.setOrientation(QtCore.Qt.Horizontal)
self.horizontalSliderFrames.setObjectName(_fromUtf8("horizontalSliderFrames"))
self.gridLayout_2.addWidget(self.horizontalSliderFrames, 1, 0, 1, 1)
self.gridLayout = QtGui.QGridLayout()
self.gridLayout.setObjectName(_fromUtf8("gridLayout"))
self.verticalScrollBarIW = QtGui.QScrollBar(Form)
self.verticalScrollBarIW.setOrientation(QtCore.Qt.Vertical)
self.verticalScrollBarIW.setObjectName(_fromUtf8("verticalScrollBarIW"))
self.gridLayout.addWidget(self.verticalScrollBarIW, 0, 2, 1, 1)
self.verticalLayout_2 = QtGui.QVBoxLayout()
self.verticalLayout_2.setObjectName(_fromUtf8("verticalLayout_2"))
self.labelMain = QtGui.QLabel(Form)
self.labelMain.setObjectName(_fromUtf8("labelMain"))
self.verticalLayout_2.addWidget(self.labelMain)
self.horizontalScrollBarIW = QtGui.QScrollBar(Form)
self.horizontalScrollBarIW.setOrientation(QtCore.Qt.Horizontal)
self.horizontalScrollBarIW.setObjectName(_fromUtf8("horizontalScrollBarIW"))
self.verticalLayout_2.addWidget(self.horizontalScrollBarIW)
self.gridLayout.addLayout(self.verticalLayout_2, 0, 0, 1, 1)
spacerItem = QtGui.QSpacerItem(40, 20, QtGui.QSizePolicy.Expanding, QtGui.QSizePolicy.Minimum)
self.gridLayout.addItem(spacerItem, 0, 1, 1, 1)
self.gridLayout_2.addLayout(self.gridLayout, 0, 0, 1, 1)
self.horizontalLayout_2 = QtGui.QHBoxLayout()
self.horizontalLayout_2.setObjectName(_fromUtf8("horizontalLayout_2"))
self.gridLayout_2.addLayout(self.horizontalLayout_2, 6, 1, 1, 1)
self.verticalLayout = QtGui.QVBoxLayout()
self.verticalLayout.setObjectName(_fromUtf8("verticalLayout"))
self.horizontalLayout_3 = QtGui.QHBoxLayout()
self.horizontalLayout_3.setObjectName(_fromUtf8("horizontalLayout_3"))
self.labelSmallIW = QtGui.QLabel(Form)
self.labelSmallIW.setObjectName(_fromUtf8("labelSmallIW"))
self.horizontalLayout_3.addWidget(self.labelSmallIW)
self.labelBigIW = QtGui.QLabel(Form)
self.labelBigIW.setObjectName(_fromUtf8("labelBigIW"))
self.horizontalLayout_3.addWidget(self.labelBigIW)
self.pushButton = QtGui.QPushButton(Form)
self.pushButton.setObjectName(_fromUtf8("pushButton"))
self.horizontalLayout_3.addWidget(self.pushButton)
self.verticalLayout.addLayout(self.horizontalLayout_3)
self.gridLayout_2.addLayout(self.verticalLayout, 4, 0, 1, 1)
self.horizontalLayout = QtGui.QHBoxLayout()
self.horizontalLayout.setObjectName(_fromUtf8("horizontalLayout"))
self.toolButtonLoad = QtGui.QToolButton(Form)
self.toolButtonLoad.setObjectName(_fromUtf8("toolButtonLoad"))
self.horizontalLayout.addWidget(self.toolButtonLoad)
self.prevButton = QtGui.QPushButton(Form)
self.prevButton.setObjectName(_fromUtf8("prevButton"))
self.horizontalLayout.addWidget(self.prevButton)
self.nextButton = QtGui.QPushButton(Form)
self.nextButton.setObjectName(_fromUtf8("nextButton"))
self.horizontalLayout.addWidget(self.nextButton)
self.gridLayout_2.addLayout(self.horizontalLayout, 2, 0, 1, 1)
self.checkBox = QtGui.QCheckBox(Form)
self.checkBox.setObjectName(_fromUtf8("checkBox"))
self.gridLayout_2.addWidget(self.checkBox, 5, 0, 1, 1)
self.retranslateUi(Form)
QtCore.QObject.connect(self.prevButton, QtCore.SIGNAL(_fromUtf8("clicked()")), self.horizontalSliderFrames.subtractStep)
QtCore.QObject.connect(self.nextButton, QtCore.SIGNAL(_fromUtf8("clicked()")), self.horizontalSliderFrames.addStep)
QtCore.QMetaObject.connectSlotsByName(Form)
def retranslateUi(self, Form):
Form.setWindowTitle(_translate("Form", "Form", None))
self.labelMain.setText(_translate("Form", "TextLabel", None))
self.labelSmallIW.setText(_translate("Form", "TextLabel", None))
self.labelBigIW.setText(_translate("Form", "TextLabel", None))
self.pushButton.setText(_translate("Form", "PushButton", None))
self.toolButtonLoad.setText(_translate("Form", "...", None))
self.prevButton.setText(_translate("Form", "<", None))
self.nextButton.setText(_translate("Form", ">", None))
self.checkBox.setText(_translate("Form", "CheckBox", None))
if __name__ == "__main__":
import sys
app = QtGui.QApplication(sys.argv)
app.setStyle('cleanlooks')
Form = QtGui.QWidget()
ui = Ui_Form()
ui.setupUi(Form)
Form.show()
sys.exit(app.exec_())
It seems like similar error happen to other people due to some "class related problems" which I have no idea about. I do not understand why it seems to work fine when I "run" in from Geany text editor, but not when I run it from terminal using python my_gui.py I get this error :
Traceback (most recent call last):
File "gui_template.ui.py", line 136, in <module>
ui = Ui_Form()
File "gui_template.ui.py", line 39, in __init__
self.setupUi(self)
File "gui_template.ui.py", line 89, in setupUi
QtCore.QObject.connect(self.prevButton, QtCore.SIGNAL(_fromUtf8("clicked()")), self.horizontalSliderFrames.subtractStep)
AttributeError: 'QSlider' object has no attribute 'subtractStep'
I also tried creating a seperate .py file in a similar fashion to how this person does it:
https://youtu.be/FcX2FsPlVeI?t=10m25s
However, I still get the same error... Any ideas?

Answer 1

The addStep and subtractStep slots are deprecated members of QSlider. They are only there to provide backwards compatibility with Qt3.
It seems you must be trying to run the example script using builds of Qt4/PyQt4 that do not include such deprecated APIs.
The documentation suggests using the setValue slot instead. But that requires passing an appropriate increment/decrement value, so it's not really a drop-in replacement (especially if you're connecting the signals via Qt Designer).
If you wanted to fix the example, you'd have to replace the two signal/slot connections with something like:
def setSlider(delta):
self.horizontalSliderFrames.setValue(
self.horizontalSliderFrames.value() +
delta * self.horizontalSliderFrames.singleStep())
self.prevButton.clicked.connect(lambda: setSlider(-1))
self.nextButton.clicked.connect(lambda: setSlider(+1))