Close window A by clicking a button on window B - python-2.7

Question

I have window A with some graphs and a button "NEXT". When the user presses the button, window B opens with some questions about the graphs on window A. It also has a button "Done". Once "Done" is pressed, window A, and B close.
Problem: I don't get window A to close and no error messages in the console.
Window A:
class Window_A(QDialog):
def __init__(self, parent = None):
super(Window_A, self).__init__(parent,flags=Qt.WindowMinimizeButtonHint|Qt.WindowCloseButtonHint)
self.setWindowTitle("Window A")
self.initUI()
def initUI(self):
# Load the images
[...]
#"NEXT button"
self.b_next = QPushButton("NEXT")
self.b_next.clicked.connect(self.open_next)
#Layout
[...]
def close_win(self):
self.close()
def open_next(self):
self.next= Window_B()
self.next.show()
Window B:
class Window_B(QDialog):
def __init__(self):
super(Window_B, self).__init__()
self.setWindowTitle("Window_B")
self.initUI()
def initUI(self):
#define text labels
[...]
#done button
self.d_button = QPushButton("Done")
self.d_button.clicked.connect(self.on_click)
self.d_button.clicked.connect(lambda:self.close())
#layout for text (questions)
[...]
def on_click(self):
Window_A().close_win()

Answer 1

In your window_B code, you do not know the reference to the correct window_A object.
So your line:
def on_click(self):
Window_A().close_win()
creates a new Window_A object, calls its close function immediately, and this objects is garbage collected asap.
You will need to pass a reference to A in the B object.
For instance:
in window_A.py
def open_next(self):
self.next= Window_B()
self.next.show()
self.next.ref_to_close_father = self
in window_B.py
def on_click(self):
self.ref_to_close_father.close_win()
This should be better (but your example is not reproducible, so there might be another problem).
By the way,
self.d_button.clicked.connect(lambda:self.close())
could simply be
self.d_button.clicked.connect(self.close)