how can I connect custom signals of different objects in PyQt?

Question

I'm not sure how to have a signal be passed between two different classes. I want classA button custom signal to show classB button !! (self.butt2.setVisible(True)) the Code is as following:

from PyQt4 import QtGui,QtCore
import sys
class A(QtGui.QWidget):
    customSignal = QtCore.pyqtSignal(str)
    def __init__(self,parent=None):
        super(A,self).__init__(parent)

        self.applyButton = QtGui.QPushButton('Apply')

        mLayout = QtGui.QHBoxLayout()
        mLayout.addWidget(self.applyButton)
        self.setLayout(mLayout)

        self.applyButton.clicked.connect(self.emitSignal)

        self.customSignal.connect(self.printStr)
    def emitSignal(self):
        self.customSignal.emit('classA')
    def printStr(self):
        print 'this is class A'

class B(QtGui.QWidget):
    def __init__(self,parent=None):
        super(B,self).__init__(parent)

        self.butt1 = QtGui.QPushButton('abc')
        self.butt2 = QtGui.QPushButton('def')

        self.butt2.setVisible(False)

        mainLayout = QtGui.QVBoxLayout()
        mainLayout.addWidget(self.butt1)
        mainLayout.addWidget(self.butt2)

        self.setLayout(mainLayout)
if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    a = A()   
    a.show()  

    b = B()
    b.show()
    sys.exit(app.exec_())

Answer 1

Assuming you want the class A button to toggle the visibility of the class B button:

a.customSignal.connect(lambda: b.setVisible(not b.isVisible()))