Traceback (most recent call last):
  File "E:\Desktop\instruments\tools.py", line 20, in <module>
    test = Test()
  File "E:\Desktop\instruments\tools.py", line 14, in __init__
    self.bar = Bar(100,100,100,200,150)
  File "E:\Desktop\instruments\tools.py", line 6, in __init__
    self.setRange(value_min,value_max)
RuntimeError: super-class __init__() of %S was never called

from PyQt4.QtGui import *
from PyQt4.QtCore import *
import sys
app = QApplication(sys.argv)
class Bar(QProgressBar):
    def __init__(self, xmax, ymax, value_min, value_max, value,  text_visible=False):
        #self.resize(xmax,ymax)
        self.setRange(value_min,value_max)
        self.setTextVisible(text_visible)
        self.setValue(value)
class Test(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.resize(100,200)
        self.bar = Bar(100,100,100,200,150)
        self.layout = QVBoxLayout(self)
        self.layout.addWidget(self.bar)
if __name__ == '__main__':
    test = Test()
    test.show()
    sys.exit(app.exec_())

    def __init__(self, xmax, ymax, value_min, value_max, value,  text_visible=False):
        super(Bar, self).__init__()  # Вероятно это вам нужно
        self.setRange(value_min,value_max)
        self.setTextVisible(text_visible)