Background estimates using ABCD method

ABCD.py

import math

class ABCDCalculator(object):
    """Class to calculate background using the ABCD method"""
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def set_x_data(self, data):
        """Give the calculator the x data"""
        self.x = data
    def set_y_data(self, data):
        """Give the calculator the y data"""
        self.y = data
    def set_x_background(self, low, high):
        """Set the background region for the x variable"""
        self.x_bkg_low = low
        self.x_bkg_high = high
    def set_y_background(self, low, high):
        """Set the background region for the y variable"""
        self.y_bkg_low = low
        self.y_bkg_high = high
    def set_x_signal( self, low, high):
        """Set the signal region for the x variable"""
        self.x_sig_low = low
        self.x_sig_high = high
    def set_y_signal( self, low, high):
        """Set the signal region for the y variable"""
        self.y_sig_low = low
        self.y_sig_high = high
    def get_background_estimate( self ):
        """Return the background estimate in the signal region"""
        return 1.*self.B()*self.C()/self.A()
    def get_background_estimate_uncertainty( self):
        """Return the uncertainty on the background estimate."""
        return self.get_background_estimate()*math.sqrt(1./self.B()+1./self.C()-1./self.A())
    def A(self):
        """Return number of events in the A region"""
        return len([(x,y) for (x,y) in zip(self.x, self.y) if\
            self.x_bkg_low < x < self.x_bkg_high and\
            self.y_bkg_low < y < self.y_bkg_high])
    def B(self):
        """Return number of events in the B region"""
        return len([(x,y) for (x,y) in zip(self.x, self.y) if\
            self.x_bkg_low < x < self.x_bkg_high and\
            self.y_sig_low < y < self.y_sig_high])
    def C(self):
        """Return the number of events in the C region"""
        return len([(x,y) for (x,y) in zip(self.x, self.y) if\
            self.x_sig_low < x < self.x_sig_high and\
            self.y_bkg_low < y < self.y_bkg_high])
    def D(self):
        """Return the number of events in the C region"""
        return len([(x,y) for (x,y) in zip(self.x, self.y) if\
            self.x_sig_low < x < self.x_sig_high and\
            self.y_sig_low < y < self.y_sig_high])

Hi
Would like to learn about this method. I have ROOT installed in my Windows 10 laptop and can run run it from Ubuntu installed in the same machine. How does this code work on data, and what is the output and its interpretation? Am a novice to this kind of work as I'm a fresh PhD student. Tried to google the ABCD method but no search is simple enough for me to quickly comprehend.
Thanks in anticipation
Phineas