PyQt4 program doesn't work

Question

The program is not working as it is supposed to. It should accept an expression and write it to the textbox above, but it isn't doing so.

from __future__ import division
import sys
from math import *
from PyQt4.QtCore import *
from PyQt4.QtGui import *

class Form(QDialog):
    def __init__(self, parent=None):
        super(Form, self).__init__(parent)
        self.browser = QTextBrowser()
        self.lineedit = QLineEdit("Type an expression and press Enter")
        self.lineedit.selectAll()
        layout = QVBoxLayout()
        layout.addWidget(self.browser)
        layout.addWidget(self.lineedit)
        self.setLayout(layout)
        self.lineedit.setFocus()
        self.connect(self.lineedit, SIGNAL("returnPressed()"),
                     self.updateUi)
        self.setWindowTitle("Calculate")

    def updateUi(self):
        try:
            text = unicode(self.lineedit.text())
            self.browser.append("%s = <b>%s</b>" % (text, eval(text)))
        except:
            self.browser.append("<font color=red>%s is invalid!</font>" % text)
app = QApplication(sys.argv)
form = Form()
form.show()
app.exec_()

But I run window appears but when I type an expression and hit return following happens:

C:\Anaconda3\python.exe "F:/Programming solutions/python/pycharmpython/GuiApp/gui1.pyw"
Traceback (most recent call last):
  File "F:/Programming solutions/python/pycharmpython/GuiApp/gui1.pyw", line 24, in updateUi
    text = unicode(self.lineedit.text())
NameError: name 'unicode' is not defined

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "F:/Programming solutions/python/pycharmpython/GuiApp/gui1.pyw", line 27, in updateUi
    self.browser.append("<font color=red>%s is invalid!</font>" % text)
UnboundLocalError: local variable 'text' referenced before assignment

please help.

Answer 1

The problem is caused by the incompatibility between python2 and python3, for example unicode is no longer present in python3. also that there is a bad handling of the exception, for example if the error occurs in the line text = unicode (self.lineedit.text ()) then the text variable will never have been defined and therefore generates another error in the line that prints the error, considering the above I have implemented the following solution that is compatible with python2 and python3.

from __future__ import division
import sys
from math import *
from PyQt4.QtCore import *
from PyQt4.QtGui import *

class Form(QDialog):
    def __init__(self, parent=None):
        super(Form, self).__init__(parent)
        self.browser = QTextBrowser()
        self.lineedit = QLineEdit("Type an expression and press Enter")
        self.lineedit.selectAll()
        layout = QVBoxLayout()
        layout.addWidget(self.browser)
        layout.addWidget(self.lineedit)
        self.setLayout(layout)
        self.lineedit.setFocus()
        self.connect(self.lineedit, SIGNAL("returnPressed()"),
                     self.updateUi)
        self.setWindowTitle("Calculate")

    def updateUi(self):
        text = str(self.lineedit.text())
        try:
            self.browser.append("%s = <b>%s</b>" % (text, eval(text)))
        except:
            self.browser.append("<font color=red>%s is invalid!</font>" % text)
app = QApplication(sys.argv)
form = Form()
form.show()
app.exec_()