I can not capture data provided in a lineEdit

Good afternoon everyone! I need to reuse the data from lineEdit's obj and obj1 in another class, but when I try to do this, I get the error: AppCAD 'object has no attribute' coord. Where am I going wrong?

import sys
import PyQt4.QtCore as qc
import PyQt4.QtGui as qg

from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure

import numpy as np
from matplotlib.lines import Line2D
from matplotlib import pyplot as plt


class AppCAD(qg.QMainWindow):

    def __init__(self, parent=None):
        qg.QMainWindow.__init__(self, parent)
        self.setWindowTitle('CAD Input Python')
        self.setGeometry(100,100,800,600)
        self.create_main_frame()      

    #botão plotar, caixa para entrada de coordenadas e canvas          
    def create_main_frame(self):
        self.main_frame = qg.QWidget()

        self.dpi = 70
        self.fig = Figure((5.0, 5.0), dpi=self.dpi)
        self.canvas = FigureCanvas(self.fig)
        self.axes = self.fig.add_subplot(111)
        self.axes.axis('equal')

        self.axes.set_xlim(-10,10)
        self.axes.set_ylim(-10,10)
        self.axes.xaxis.set_major_locator(plt.MultipleLocator(5.0))
        self.axes.xaxis.set_minor_locator(plt.MultipleLocator(1.0))
        self.axes.yaxis.set_major_locator(plt.MultipleLocator(5.0))
        self.axes.yaxis.set_minor_locator(plt.MultipleLocator(1.0))
        self.axes.grid(which='major', axis='x', linewidth=0.75, linestyle='-', color='0.75')
        self.axes.grid(which='minor', axis='x', linewidth=0.25, linestyle='-', color='0.75')
        self.axes.grid(which='major', axis='y', linewidth=0.75, linestyle='-', color='0.75')
        self.axes.grid(which='minor', axis='y', linewidth=0.25, linestyle='-', color='0.75')
        grid = qg.QGridLayout()
        self.buttonA = qg.QPushButton("Plotar")
        self.obj = qg.QLineEdit()
        self.obj1 = qg.QLineEdit()
        self.connect(self.buttonA, qc.SIGNAL('clicked()'), self.press_buttonA)
        self.main_frame.setLayout(grid)
        self.setCentralWidget(self.main_frame)   

        grid.addWidget(self.buttonA,4,0)
        grid.addWidget(self.canvas,0,1,3,3)  
        grid.addWidget(self.obj, 0,0)
        grid.addWidget(self.obj1, 0,1)
    # Coordenadas -------------------------------------------------------------
    def i2o_coordenadas(self):
        self.coord = []
        cx = float(self.obj.text())     
        cy = float(self.obj1.text())
        self.coord.append([cx,cy]) #Aqui o programa deveria salvar as coordendas dadas pelo usuário na lista self.coord

     #plotagem          
    def press_buttonA(self):

        px = self.coord[0]

        py = self.coord[1]

        self.axes.plot(px, py, marker='o', color='black', markersize=7.5, linewidth=0, zorder=13) #aqui o programa deveria utilizar as coordenadas para plotar no grafico, via matplotlib

def main():
    app = qg.QApplication(sys.argv)
    form = AppCAD()
    form.show()
    app.exec_()

if __name__ == "__main__":
    main()